matrix of all possible differences

Question: I need to compute the matrix of differences of a vector, just like here in section "Matrix of differences". Is that actually correct? I thought that, in order to add up (or subtract) two vector/matrices they had to have the same dimensions.
Answer: That's not a "real" matrix/vector difference. It's just a particular operation, a non-standard way to represent inside a matrix all the differences between the components of two vectors.
If you want to write it using correct/standard matrix operations, you could write
$A = u x^t - y u^t $
where $u^t = (1, 1, 1... )$ is an all-ones vector, and $x$, $y$, are your vectors, represented as column matrices.
Answer: It is correct as written, but it's a notational problem. Usually one uses a symbol to denote that we are interested in the matrix of differences, perhaps something like $(u,v)_{diff} = $ some matrix.
On the other hand, you are correct - when adding or subtracting matrices, they should be of the same dimension. I would say that his use of the simple minus sign is a slight abuse of notation here, but that happens from time to time.
Answer: You are not "really" taking the difference of two matrices, at least not in the sense of addition of matrices (which usually requires the two matrices to be the same size).
Instead, the "$-$" symbol here represents a different operation (alas for the confusion), in which you consider to $n$-tuples and construct a matrix whose entries are all possible differences. So the $-$ symbol you are seeing is not the symbol that represents subtraction of matrices in the usual sense.
If we use a different symbol, say $\ominus$, it might be clearer. We define $\ominus$ as an operation that takes an $n\times 1$ vector and a $1\times n$ vector, and whose result is an $n\times n$ matrix, as follows:
$$\left(\begin{array}{c}a_1\\ \ldots\\ a_n\end{array}\right)\ominus \left(b_1,\ldots,b_n\right) = \left(\begin{array}{cccc}
a_1-b_1 & a_1-b_2 & \cdots & a_1-b_n\\
a_2-b_1 & a_2-b_2 & \cdots & a_2-b_n\\
\vdots & \vdots & \ddots & \vdots\\
a_n-b_1 & a_n-b_2 & \cdots & a_n-b_n
\end{array}\right);$$
that is, the $ij$th entry of $\mathbf{v}\ominus \mathbf{w}$ is $v_i-w_j$.

matrix of all possible differences


What is band filling effect?

Question: Could anyone tell me what is band filling effect? I have search Physics.stackexchange and Google, but didn't find any useful information. I'll appreciate it if anyone can tell me the physical image of band filling effect.
Answer: This effect leads to a blue-shift of the luminescence, absorption, gain spectra of semiconductors with increasing of the concentration of carriers. It happens because of occupying of low-energy states of energy bands by particles. Consequently, due to the Pauli exclusion principle, transitions between occupied states in valence and conduction bands are forbidden and the possible transition, in this case, appears for higher photon energies only (higher comparing with the band gap).
Takahiro Numai, "Fundamentals of Semiconductor Lasers" (see p. 119)
see also Fig. 13 here http://online.lesn.lehigh.edu/courses/mat435/lectures/nonlin/non1.htm
Comment: Thanks very much! I'll refer to the references you provided in details.

What is band filling effect?


Bike size advice Bianchi vs Cannondale

Question: I have been after a Bianchi Via Nirone 7 for more than one month and an half without much success. The main reason is that they don't produce many 47cm frames, while 47cm would be my optimal size.
In the meantime, I ordered also a Cannondale CAAD Optimo 48cm and it fits fine, it's arrived in the shop ready to be brought home. But I really want the Bianchi. The problem is that the cheapest 47cm upgrade that I can do with a Bianchi is the double of my budget (Sempre Pro).
At this stage I'm very exhausted and temped to go for a via Nirone 7 50cm frame even if is going to be slightly too big for me.
I already quickly tried the 50cm via Nirone and the hip isn't very stable, I do some small overstretch.
If I go for a 50cm frame I need to cut 2cm in the seatpost (seatpin). So, the saddle would be slightly lower than handlebar.
However, watching the geometries of Bianchi Via Nirone 7 50cm and Cannondale CAAD Optimo 48cm I don't see much big difference. My leg inseam is 70cm and height is 159cm.
Bianchi Geometry:

Cannondale Geometry:

By the way, I did two 50 mile rides on Trek Domane, the first with a 47cm frame and the second with 50cm, and I felt more comfortable with 50cm. (But there wasn't any need of cutting the seatpost - I put it at the lowest position).
Trek Geometry:

Would would you do in my case? - Any advice?
Comment: Why can't your local bike shop order you a 47cm frame and build up the bike?  Are you limiting yourself to just in-store inventory?
Comment: Wait, save up, get the bike you want.  You're going to own it and ride it for decades.  If you compromise on the essential things then you'll not love the bike as much.    You could potentially take the 40% discount and buy stuff like wheels and components, but search for the frame you want, regardless of the source.
Comment: I think this is purely a matter of opinion. You seem to want the Bianchi so much that you're prepared to put up with it not fitting very well. We can't know how much difference the size difference really makes to your body, so we can't rally give any objective advice.
Comment: I have a 40% discount if I go with that specific retailer. I spoke both with them and Bianchi and the problem is Bianchi, if I go with another retailer it won't change anything.
Answer: When you buy a complete bicycle, you just need to check two things: fitting and components.
Did you test the 2 bikes in the size you are discussing? The Bianchi should have a better frame, but nothing that can counterbalance the fact that a 50cm frame is too big.
Regarding "If I go for a 50cm frame I need to cut 2cm in the seatpost (seatpin)" I would go as far as to say that you are voiding warranty and therefore it does not make sense to do so on a new bike. In my opinion, neither on a used one.
Comment: Cutting down a seatpost is something that a bike shop will do quite often. Some bikes just don't have that much adjustment before the post bottoms out in the frame.
Comment: The Via Nirone 7 looks like a entry level aluminum frame to me. Why would anyone want to modify one instead of keep an already existing and fitting Cannondale?
Comment: @Carbonsideup : I understood the OP wanted to cut the seat tube. I hope I am wrong and you are right.
Comment: @ojs I am not sure if it is only marketing, but the Via Nirone 7 should have a Bianchi fork with carbon inserts that make the ride smoother. Does the fork alone justify the price and all the hassles of modifying it? I doubt, but a road test is necessary to have an opinion. Or maybe the OP just like the look of the Bianchi: I agree with you, a good custom paint job on a Cannondale is still preferrable (and probably cheaper) ...
Comment: @EarlGrey it is only marketing, and forks are fairly standard so you can just replace the one on Cannondale if you want.

Bike size advice Bianchi vs Cannondale


Does leaving a capo on "hurt" the strings?

Question: On occasion I've accidentally left a capo on (overnight). Does this decrease the life of the strings, staying in tune time, hurt the neck, or anything else that's bad?
Answer: I would certainly not leave the capo on my fretboard when not in use. I cannot say it visibly hurts the neck for sure but it does wear out the strings. Here is a wonderful piece of advice from Lee Griffith in his article, A Capo is a Wonderful Thing:

One caution is important to mention. Do not leave the capo on the
  instrument when not playing it. The capo, when clamped on the neck,
  holds the strings down on the fretboard and creates extra tension
  on the neck and the top of the guitar. All acoustic guitars are
  destined, at some point in time, to have problems due to the
  tension of the strings. Why hasten the process by leaving a capo
  clamped on your guitar?
Comment: I doubt the capo adds much tension to the strings. If this was really a problem then we'd be detuning our guitars every time we're done playing.
Comment: I know what you meant, I just think you're exaggerating the amount of tension added by the capo.
Comment: @Brian Ortiz: Eh... I myself have left my capo on overnight on several occasions. But it's not about the tension to the strings but the extra stress on the neck *due to* the increased tension in the strings, which could be significant, depending on where the capo is placed. One certainly doesn't want to have the capo perpetually hugging the neck.
Comment: @Brian: But, yes, it's not really about string life, here...
Comment: @Brian: Oh, I see... but I merely posted up Griffith's. That wasn't really my opinion :) but just so my answer could have more weight. Anyway, I just don't leave the capo on unnecessarily too long, just as I don't keep my bass plugged in when I'm not playing! But really, if one leaves the capo on every night, if the strings have a phosphor coating, that will begin to crack right at that fret and strings may probably have to be changed faster. I never keep the capo on anyway, since I always clean my fretboard after each session...
Comment: I would be very surprised if use of a capo added more tension to the neck than just going up to the next string gauge.
Answer: My question is, why do you want to leave the capo on the guitar all the time? To keep the guitar in a higher-than-normal pitch, or to lower the action?
A properly set-up guitar will have very low action without buzzing, equally as low as you'd get with a capo in place. It is also a lot more fun to play.
If you want higher than standard tuning, then take the guitar to your local guitar-repairshop and talk to the head tech. Tell him you want to keep your guitar in a higher tuning than normal but don't necessarily want to keep using a capo to achieve it. They can suggest lighter-guage string brands you can tune a bit higher, and then tweak the guitar so any increased string tension won't raise the action. The idea with the lighter gauge strings is to help reduce the tension at the higher pitch, but odds are good you'd have to have a minor tweak to keep the action feeling nice and comfortable.
The only times I'd use a capo is to get a particular sound, since stopping the strings at the 5th, 7th or 12th fret sounds very different than completely open strings. Or, because a particular song calls for it because that's how the original artist played it.
Comment: People are lazy. You don't necessarily _want_ to leave it on, but you do so nonetheless. I tend to leave the capo on if I use it just before I put away my guitar.
Comment: Agreed- except for where you say that a properly set-up guitar will have equally low action as one with a capo in place.  No matter how low the action is, the capo will lower it further.
Answer: I personally would expect the most damage might actually be to the capo, because I would expect that prolonged contact with the strings might cause permanent grooves in the rubber or soft plastic pad of the capo, similar to what might happen if you were to hold a chord shape with your fingers for the same amount of time. I don't know about others, but my finger tips show signs of wear after playing four sets at the bar. I think a capo might also.
Answer: We can concoct reasons why minimal damage might result.  But the real-life answer is, no it won't do any harm to the guitar or its strings.  And have any of us ever had to replace a 20-year-old capo because of wear?
Answer: I think the main problem with leaving the capo on for any longer than needed is that the capo will wear the strings into the frets causing "tracks" in the frets...
Comment: That seems unlikely to me. Fret wear is caused by the strings _rubbing / clashing_ against them. Constant firm downwards pressure should not cause significant wear.
Answer: I leave it on all the time so I know where it is. The guitar is a 17 year old Taylor which sits on a guitar stand in my room.The capo might develop groves but then you can see exactly where to place it when moving it up or down a fret without affecting tuning or intonation.


How can we attract experienced TeX hackers to participating on this website?

Question: As pointed in the comment below there are two =) I wish for Knuth to pop in here one day ;-)
Comment: Knuth [doesn't even use email](http://www-cs-faculty.stanford.edu/~uno/email.html)! There are [at least](http://tex.stackexchange.com/users/73/joseph-wright) [two](http://tex.stackexchange.com/users/179/will-robertson) LaTeX hackers. A way to rephrase this into a more meaningful question: *How can we attract experienced TeX hackers to participating on this website?*
Comment: There's also Taco Hoekwater, http://tex.stackexchange.com/users/89/taco-hoekwater
Comment: i think @herbert voss qualifies; hope i haven't given away any secrets.
Answer:
Quality is attractive, make it public visible. If have a blog, write about excellent questions and answers on the site, quality is attractive. You could even post a story on hacker news, reddit, or stumbleupon. Share links to great questions.
Seeing an own difficult question answered here, is attractive. If you notice that a TeX hacker raises a question via twitter, facebook, mailing list, Usenet, or web forum and you see there's no good answer yet, post the question here. Help her or him to get the answer. Of course include a link to the source.
Make package authors interested by questions and answers which can improve the package or the class.
Directly invite TeX experts, for example as interviewee or guest author in our upcoming TeX.SX blog.
Go where the TeX experts are, show up at TeX conferences and local user group meetings, talk about TeX.SX.
Comment: Re @MartinScharrer's first comment: `status-completed`.
Comment: Nice. Any chance getting e.g. Heiko Oberdiek onto this site? Herbert and Ulrike are already here as well ...
Comment: @Martin: I also had that idea and mentioned him in the [inviting authors for blog posts](http://meta.tex.stackexchange.com/questions/1460/what-would-you-like-to-read-in-a-tex-sx-blog/1489#1489) proposal - perhaps he would like to talk about his big bundle project.
Comment: Is the bundle not just for easier upload to / maintainability  on CTAN? (I started to think to bundle my smaller packages as well for just this reason, but didn't dared to ask for a place on CTAN.) Some packages are very related and depend on them as well, so it makes sense to only release combined updates.
Comment: @Martin: I guess so. However, I noticed several times that a user wasn't able to install a package (for instance with MiKTeX) just because he did not find it in the package manager, as it was part of a bigger bundle.
Answer: I think building up the reputation of this site as a - nay, the - place to get high-quality answers to *TeX questions will be a major factor. Any experts who are interested in answering questions at all will probably want to be associated with the best site out there. And any experts who aren't interested in answering questions, well, we weren't going to get them anyway. Obviously, we're not going to spring out of private (or even public) beta with that reputation already built, but what we need to do now is make the decisions that will guide the development of the site in such a way that we're setting it up to be the best resource on its topic.
Besides that, it's probably mostly a matter of using our connections. As mentioned, there are a couple of real live LaTeX hackers registered and perhaps they know other people who would be interested in a site like this. Many of the rest of use are probably in academic environments, which means we're likely to have a lot of contact with other people who use *TeX and perhaps even have written packages for it. They'd be valuable resources for the site, if they're interested.
Answer: Improve the interface. I want to see a threaded interface in date order (latest last), with topics I have read or skipped greyed out. It needs to show only the OP of each thread by default, with the conventional [+] to expand and [-] to contract. In fact, I'd like to read the site like a Usenet newsgroup :-) but keep the vote-based ranking.
P
Comment: Ain't gonna happen. And it's really not intended to be like a Usenet group, so this is a case where I think you need to adapt to the interface, not the other way around.  It's different, not worse, IMO, and once you get used to it, it works quite well. In particular, it's designed to be much more archival than a Usenet group, and this is one of its strengths. But that very property doesn't fit so well with more dynamic way that a Usenet group works.
Comment: We don't have any influence on the actual interface. The site is provided to us by the http://stackexchange.com people and identical for the dozens of their sites. Adjustments are limited to the styles (colors, background images, default syntax highlighting, etc.)
Answer: On the other hand, Knuth has a mathoverflow t-shirt!
Comment: If this site ever makes t-shirts, we should give him one!
Comment: Now _that_ photograph would make good copy!
Comment: Now that there are TeX.SE shirts http://meta.tex.stackexchange.com/questions/1837/tex-stack-exchange-swag-for-top-users it would be great to send him one.


At what age should I explain to my kids that we don't believe in God?

Question: I've been wondering about this. Me and my partner (I'm gay) are thinking of adopting soon.
Comment: While a valid question, if you are only at the 'thinking of adopting soon' stage, there's probably some other higher priority things to consider. ;)
Comment: I don't think it should be offensive. This is a childs life we're talking about. I don't think lying to a child is fair. If I teach them to see validity in things that can't be proven then they can be very disappointed in life.
Comment: I'm not religious myself, but I think your question is going to be offensive to those who are which is not what this forum is about. I think you have a fair parenting question, but it needs work.
Comment: @lo-fi I have rolled back your question to its first version. Please find a way to include the relevant information without belittling those who believe differently than you, as comments like that are not allowed on our site. We have a strict policy of playing nice with others, and questions or answers should not be used as [soapboxes for personal beliefs or agendas](http://meta.parenting.stackexchange.com/questions/34/whats-the-best-strategy-to-combat-soapboxing).
Comment: To clarify, do you want to impose your belief (that God doesn't exist), rather than let the child come to their own conclusion? What age child do you intend to adopt? Please update your question to include these details.
Comment: Probably when he or she will ask you about God
Comment: David Sedaris's experience of attempting to communicate the tenets of faith across cultural and religious boundaries may be relevant: https://m.youtube.com/watch?v=N5apZmwR9UI
Comment: Edited to answer your questions.
Comment: @lo-fi If I understood correctly, you are saying that telling a child that God exists is the same as lying to him/her. I am agnostic/atheist, and still I find that your very comment is offensive toward believers.
Answer: I can't imagine that teaching a child that God doesn't exist is, at it's heart, any different than teaching a child that God does exist.  I have some very dear friends who do not believe in God.  Really, it's a simple matter of they don't attend church, they observe some holidays (such as Christmas and Easter) from a purely secular standpoint (Santa Claus, Easter bunny, etc.).  I imagine that, at some point, the question may come up from their boys, "Why does my friend believe in God and we don't?" or something from that perspective, but I don't see that there's any reason to call attention to the situation until/unless a child brings the topic up first.  At that point, you will have to thoughtfully consider how to answer the question.  I would hope that you wouldn't want to imply to your child that those who are religious are stupid or ignorant because of their beliefs, so you would have to choose your words carefully--in the same way that a parent who did believe in God might someday have to address the question of why one of their friends doesn't believe in God.  I mean, do you really want to possibly sacrifice a personal friendship or one of your son's friendships because of a difference in beliefs?  I would never want my child to believe that his friend or his friend's parents are bad or ignorant people because they don't choose to follow my family's belief system.
But I think that the reality is that if a child isn't exposed to a God-centric belief system, they are unlikely to construct one on their own.  My oldest is 5, we are Christians, we have friends and family who are not who also have children around his age.  They play together and have never discussed God to my knowledge.  I expect eventually the topic will come up (especially with my nieces who are being raised--well, truthfully, I don't know what they're being raised exactly), but I don't plan to bring it up unless my children do.
Depending on the diversity of where you live, your child may never ask why your family's beliefs are different from those of his friends and acquaintances.  In other areas, like where I live, the beliefs are somewhat more homogeneous which may draw more attention to your child's differences.  This might cause him/her to ask questions sooner rather than later.  Either way, I don't think the question is so much how to teach them that God doesn't exist, but rather how will you respond when they ask why their beliefs are different from others.
ETA:  It occurred to me after responding that you said you were thinking of adopting which could add a whole new angle to the situation.  If you adopt an older child, there may be some unlearning to do.  In which case, being able to clearly articulate to a young-ish child (say, pre-school age) why you and your partner do not believe in God will be more important.  At first, it may be a simple thing of not going to church, but if a child remembers attending church/mass/temple/etc. at some point, then he/she might eventually ask why you don't.  I don't know your personal reasons, but keeping it short is probably the best way to address the situation:  "We don't believe in God because we can't see God or speak with God or touch God" or whatever your reasons.  You can get into other more metaphysical and metacognitive discussions about it when your child is older.  This is how we approach teaching our children about God--at their age, the concepts are very simple, but progress in depth and breadth as our children grow older and their cognitive development can process the information better.
Comment: @dave one does not have to frame it as a belief system to communicate that people believe in different things. For instance, in our family, we simply state 'mom believes this, dad does not'. That, in and of itself, communicates that people believe different things--including some that don't believe it at all.
Comment: Our children are being raised as Muslims in a historically Christian country (Australia). Children start getting bombarded with Christmas (religious and santa) from the age of 4. It becomes an issue quite early on. I agree that atheism should be framed as a belief system in any such discussions if only to make it easier to explain that different people believe different things.
Comment: This is a (well-put) long way of saying "let your actions speak for you," which is a great answer.  If something exists (and is important), your kids will know because you'll talk about it.  And the other way around.
Answer: First, I think that it is important to think about what it is that you actually want to teach. Atheism is not in and of itself a belief system, it's a metaphysical position. Theism is also not a belief system. A "system" needs more than a single metaphysical point.
So what system of beliefs do you want to teach to your child? You're going to have to teach them something, even if that something is "people believe different things for different reasons and I am personally okay with that because people have a right to believe different things." That's much closer to a system of belief than atheism, because it involves ideas about rights and tolerance and other stuff that is outside of the single metaphysical point of whether or not god(s) or goddess(es) exist for some given definition of gods and goddesses.
So if your belief system is something like secular humanism, you teach your child the principles--be kind to others, show empathy, lying hurts people, stealing hurts people, etc.-- and give them the secular humanist rationale as is age appropriate. At some point they will become aware of the question of whether supernatural things are real or not, which is a different question.
For example, when a child becomes aware of death, they may ask what happens to people when they die. It is really hard to avoid questions about whether there is or is not a god when discussing the possibility of the afterlife. I think that the thing to do in that case is to be honest and sensitive and explain what you think, and that other people think different things. I haven't really had my kids pursue me on why other people think different things. My daughter, who is 4, took that as permission to think something different herself, and decided that when people die, they come back as babies. Now she has decided that this is something that only happens "in the story", although which story that might be is somewhat unclear to me.
The question of god also comes up when well meaning Christians--apologies to the Christians, but I simply haven't been actively proselytized by any other religious group--tell your children that they should believe in god and give them religious material to view. In that case, if they are very young it helps to just treat it like you treat stories about Santa Claus or any other mythical characters. When my kids asked about Santa, I always turned the question around ("Well, what do you think) and that worked out pretty well--they believed for a year or so and then decided that Santa wasn't real. They've never asked about Jesus, possibly because he doesn't bring presents and is therefore less immediate.
The short answer, in other words, is that you talk to your kids about deep topics when they ask, and as much as you responsibly can, you let them figure it out for themselves.
Answer: All you need do is not teach them that God exists. If (when) they hear about God from elsewhere say something like "Some people believe in this God thing, but we don't. When you get older you will be able to make up your own mind, and look into it more if you want. But we don't believe in it so we're not going to make you go to church or anything."
I think thats a better approach than preaching atheism, if you get what I mean. For a start, as a child grows they will want to rebel. What better way to annoy Dad than dating a Catholic (Muslem, Hindu insert faith as appropriate)?
Answer: I think your best bet lies in teaching your children what you do believe or think, rather than what you don't.  Not that there aren't times when you'll need to explain that something's not true, but it's generally more powerful to give your child the tools they need to determine what's true.
Children make wonderful scientists because of their curiosity.  Nurture that.  Don't settle for giving them answers like "that's just the way it is", and when they tell you something try asking them to explain why it's so or how they know it's true.  When you can explain your lack of belief in a god in these same familiar terms, it will make sense to them.
Try to avoid prejudicial criticism like "Christians are stupid".  One day your child will meet a nice, smart Christian and realize you lied.  Instead use reasoned, specific criticism.  Talk about who you disagree with, why you disagree. Give your child a chance to ask questions or raise objections, and address them seriously.
Answer: In our kid's school they teach them about a wide range of religions (Islam, Christianity, Hindu, Sikh etc) and while the school itself is slightly Christian, they support children in learning why their friends may have different beliefs than them, so my son, who is atheist/agnostic has a amongst his friends a couple of Muslim, one Hindu, a few Christians and some others who don't believe in any religion.
They don't see this as weird - it's just the way things are, like some have ginger hair and some don't. Some have different sexuality. Some have 1 parent, some have 2 the same sex etc.
They start to bring these teachings in around age 5 (not in much depth until a few years after that) and it doesn't actually start with religion - it begins with tolerance and an understanding that everyone is different.
Teaching them that god does or doesn't exist isn't necessary at this age - just give them a tolerance structure and enough information for them to work their own way. I'm definitely an atheist, but I give my kids enough room to decide when they are older.
Answer: First, consider the methods.
To teach that a specific god exists, you would typically raise your child as a member of a particular church.
To teach that 'god' doesn't exist, I see two primary options:

Don't bother joining a church. They'll figure stuff out on their own eventually.
Teach theology. Having a broad understanding of religion on the planet will likely lead them to a conclusion you'd be happy with (even if it's not atheism).

For option 1, you'd obviously be able to start that 'non-teaching' at day 1. For option #2, I don't think there is any one answer there. That's really going to depend on you.
Comment: Point 1 seems very sensible. Address cultural issues, Father Christmas, God, the Tooth Fairy, Freedom, etc as they come up.
Answer: We did it (gently) as soon as he started asking about Jesus - he went to a religious preschool in part so we could get this nonsense out of the way earlier.  You know: Everyone has different beliefs but mommy and daddy believe this because of these reasons.  Do you think Santa Claus is real or pretend?
Answer: I don't believe in teaching my beliefs to my child. I believe in talking about whatever interests my child in an adult manner. When my son asked me: "What is 'religion'?", I tried to explain my perception of the matter to him. He knows about the big bang, so when I said that some people believe that God created the universe, he replied: "But that is not true, it was created by the Big Bang." I said that I agreed with him, and that this seems the most probably theory to me, but that we don't know for certain, because no-one has been there and witnessed either. I don't usually bring up topics that my son is not currently interested in. And I try to give him all the facts I have, discussing their relative merits, and giving him the opportunity to chose his own interpretation. After all, I don't need him to be a sceptic like me. If he wants to believe in God, why not? But then I guess that this practice will make him a sceptic ;-)
You will of course chose your own message you want to convey, and the above was only meant as an illustration of what would be the best manner for all kinds of parents, independent of their beliefs:

talk about what interests your child when it interests him or her and don't force topics on them that are irrelevant to them at the moment and won't reach them
talk to them like you would to an adult; use words your child knows, but don't simplify the matter - children are able to deal with not understanding everything at once and will come back asking for more details, when they are ready
Comment: Not a bad answer, but it feels you might be blurring science and religion there.
Answer: We simply didn't go to church, pray, or talk much about God in our home because, well, being atheists, God and religion aren't an issue we spend time on.
Round about second grade, it came up with our oldest. She asked what church was, and why people went there. I think it was annoying that so many of her friends were unavailable on Sundays. We told her some people believe there's a powerful being called "God" that created everything and watches over everyone, but that mom and me had never seen any reason to believe that was true, and that her friends went to church to pray to and sing to God.
It never really came up again, until she became politically aware, and became disgusted at the way fundamentalists push their beliefs into public policy.
(Yeah, trying to force everyone to live a Biblical lifestyle is forcing religious beliefs into public policy. Live your life according to your beliefs, and let others do the same.)
Little sister seemed to figure it out, or perhaps she asked big sister, because she's never brought it up with us. She's the fourth family science nerd after me, (math/physics), mom (biology/chemistry/medicine) and big sister (conservation biology).


Tridion 2009 Set Metadata field value in C#

Question: I have hundreds of pages that are using the same page metadata and I would like to set an specific value in one of this fields that is a text with C# or other automatic way.
Does anyone knows how to do it?
Thanks in advance.
Comment: Do you want to set a default value, or just update all the Pages with this metadata Schema and set a specific value for one of its fields?
Comment: The second part. I need to update all the pages that has this new page metadata field.
Answer: On Tridion 2009 you should use the TOM Interop APIs (COM) which are provided under Tridion\bin\Client\PIA. You'll need to use the Tridion.Interop.TDS.dll and Tridion.Interop.TDSDefines.dll.
Create a new Tridion session with code like this:
TDSE tdse = new TDSE();

If the current Windows user is a valid Tridion user, then it will just work. If it's not it's a bit more complex, you need to run under a valid Impersonation account, then call tdse.Impersonate("accountname").
Then you need to find all pages that may contain the value - you probably want to do something like a "Where Used" on that schema that gives you all the pages:
Schema s = (Schema) tdse.GetObject("tcm:123-99-8", EnumOpenMode.OpenModeView, Constants.URINULL, XMLReadFilter.XMLReadNull);
ListRowFilter filter = tdse.CreateListRowFilter();
filter.SetCondition("ItemType", ItemType.ItemTypePage);
XmlDocument doc = new XmlDocument();
doc.LoadXml(s.Info.GetListUsingItems(ListColumnFilter.ListID, filter);

Now you have an XML Document that contains all the IDs of all Pages that use the schema you loaded ("tcm:123-99-8" in the example above).
Next, you need to load each individual page in a loop, get the fields, update them, save the page, move on to the next. Something along these lines:
foreach (XmlNode node in doc.SelectNodes("/tcm:ListUsingItems/tcm:Item", nm))
{
    Page page = tdse.GetObject(node.Attributes["ID"].Value, EnumOpenMode.OpenModeEdit, Constants.URINULL, XMLReadFilter.XMLReadData);
    ItemFields metadata = page.MetadataFields;
    string somevalue = metadata["FieldName"].value.ToString();
    metadata["FieldName"].value.Add("New value");
    metadata["FieldName"].value.RemoveAll();

    page.Save(true);
    if(page.Info.IsCheckedOut)
        page.CheckIn();
}

I haven't tested that code, just found it lying around in an old project...
EDIT As Bart suggests, all these COM objects should be released with Marshal.ReleaseComObject(comObject);
Comment: When using TOM Interop, don't forget to release the System resources to prevent memory leaks, see http://tridion.stackexchange.com/questions/1207/event-system-alternatives-memory-leakage/1216/#1216 for more details.
Answer: Since you are on version 2009 your options are a bit limited, you would either use the Business Connector (SOAP) API, or the TOM API directly on the server.
For the TOM API you could write a ASP Page, or you can do an ASPX Page (with C#), but then you have to use the TOM Interop, and run it from the Custom Pages. I don't think I have any direct examples of how to do that, it has been more than 3 years ago since I wrote stuff like that.
Probably not what you wanted to hear, but I would suggest upgrading to SDL Tridion 2013, and then you can use the Core Service to easily write an application in C# to suit your needs. You will also find a lot more examples online on how to do such things.


In Pokemon GO, what are my Pokemon's hidden IV stats, and why do they matter?

Question: I've been hearing talk about hidden stats called IV, and I also hear they may override CP when it comes to long-term battle effectiveness. Is there any validity to this?
Comment: Would be nice if they put it in game, but for now I am using [this site](https://pokeadvisor.com/) to see my IV stats which can sort your Pokemon by IV%. Here is the [Reddit page](https://www.reddit.com/r/TheSilphRoad/comments/4vdm93/pokeadvisorcom_automatic_stats_calculator_and) for more info
Answer: When talking about IV vs CP,

Combat Power is only an average of your Pokemon's stats and is only a rough estimation of a Pokemon's strength. -source

There are 3 IV's that we know of; Attack, Defense, and Stamina. Defense and Stamina are important when it comes to defending in gym battles, and Attack and the move you are attacking with's base damage and attack speed are important for attacking gyms.
So for defense of gyms, a Pokémon with a lower cp but higher Defense and Stamina may be a better pick than a  higher cp Pokémon who just has really high Attack. For attacking, you will want to prioritize Pokémon with higher attack and lower defense, as you can always dodge to avoid taking a lot of damage. See here for more info.
Also, see here or here for an IV calculator.
Comment: @unionhawk And now we have two, just in case one goes down.
Comment: The more info is a nearly useless page of yatter.  This answer does not say why they matter, beyond vague generalities.  'If your pokemon has 10% higher attack,mits attacks will deal 10% more damage' is an example of a concrete description if why attack stat matters.
Comment: -1, for these criticisms: All three stats are equally important on offense as they are on defense. Furthermore, CP is an amalgamate of the three stats *plus their level modifier,* a coefficient of each of the three stats. A Pokémon with lower CP will not, generally, exhibit more power on the merits of higher IVs; its actual, level-adjusted stats will still usually be lower.
Answer: IV stand for "Individual Value". They are hidden stats, which differ from Pokemon to Pokemon you hatch or catch. IVs stay constant when evolving or powering up a Pokemon. IV will influence how "strong" your Pokemon will become at each upgrade stage. IVs are therefor a key measure when deciding which Pokemon to upgrade.
An elaborate explanation of IVs can be found on reddit thread. For convenience, here the example which is given in the thread:
Every Pokemon has Attack/Defence/Stamina Stats.
IV are the hidden Stats that can differ from pokemon to pokemon and go from 0 to 15 for each Stat (Attack/Defence/Stamina).
Lets take Charmander as an example.
Those are his ingame Stats:
BASE STAMINA 78
BASE ATTACK 128
BASE DEFENSE 108
But each time you hatch/catch a Charmander, it gets hidden Stat Rolls to Attack/Defense/Stamina that we call IV (Individual Values) and go from 0 to 15 as I stated above.
Lets say you get 12/7/14 as an example. That means your Charmander gets 12 Attack, 7 Defense and 14 Stamina added to his base stats, for a final result of 90 Attack, 135 Defence, and 122 Stamina.
IVs raise a Pokémon's maximum potential, so although a 600 CP Charmander will preform better than a 500 CP Charmander and take less stardust to upgrade to maximum level, a lot of people would prefer a 500CP Charmander with, for example, rolls of 14/12/15 over one with 600CP that had bad rolls of, say, 7/6/10. This is because the 500CP specimen could eventually be grown into a more powerful fighter than the 600CP one ever could.
Comment: This answer does not say what the values do
Answer: CP is a number that is derived from underlying stats the Pokemon Go engine uses for Pokemon combat.
The four stats are attack, defence, stamina and level.
Each type of pokemon has a base atk, def and sta.  In addition, each pokemon has an individual variation, or IV, of 0 to 15 on each of those 3 stats.
A high IV pokemon thus displays a higher CP at the same level.
Level is what you are buying when you power up a pokemon, at +0.5 each power up.
Now, what do those stats do?
Your damage is roughly:
some constant × move dam (number displayed next to move) × atk stat × (level+some other constant) / other pokemon's def

Thus is not quite accurate, as a 0 damage move actually does a tiny bit of damage.
Your HP are (level+some constant) × stamina × some_other_constant
In short, +10% sta means +10% HP, +10% def means you take 10% less damage, and +10% atk means you deal 10% more damage.
There are other factors. +25% damage if your move type matches your pokemon type (STAB: same type attack bonus).  +25% if your move is super effective on the target (based on move type and target pokemon type),  -20% if your move is not very effective (ditto).
As it happens, basic attacks vary in damage per second.  They peak around 12, before STAB or Super Effective.  This is almost unrelated to their move damage: a 12 damage 1/second is same dps as a 6 that is 2/second.  The UI does not display the attack delay.
Finally, while CP is derived from atk/def/sta/level, it is a relatively random formula that only vaguely tracks actual combat powess.  I believe it is basically ATK * sqrt(DEF*STA) * Level * Constant, with some very small additional factors that cause it to be very slightly non-linear.  This over values ATK ompared to other stats by a factor of sqrt(ATK).
Atk/sta/def for each type can be found online.  IV calculators that take level estimates and cp values and hp and reverse engineer atk/def/sta also exist.
Comment: Thank you for providing the link between the IVs and the visible stats!
Answer: Basically, IV is a hidden set of stats that someone found in the code that determines the absolute quality and power of your Pokemon. It's really important because it implies that CP isn't the only thing going into how strong your Pokemon will be fully leveled/evolved. You may find you have been trashing super strong Pokemon with not quite as high of a CP.
Basically, you need an IV calculator, and you need to put those stats against your Pokemon's base stats to figure out how powerful it actually is.
Here's an IV calculator that works for a mobile phone: https://pokeassistant.com/main/ivcalculator
Answer: My understanding of IVs is that they act as 'bumps', randomising the stats of Pokemon slightly. If it weren't for IVs, every Pokemon would start out with the same stats and would reach the same stats when fully powered up; two Pokemon of the same species who had been powered up to the same degree would be equally powerful (different moves aside).
IVs nudge those stats slightly, so two Pokemon powered up to the same degree might be slightly (or not so slightly) different. Since you can power up any Pokemon, but IVs are immutable, it makes sense to look for a Pokemon with high IVs, even if they aren't as powered up as other Pokemon with lower IVs.


Using AD as a general purpose directory

Question: Is there anyone using AD as a general purpose directory (meaning for uses other than domain authentication / authorisation and stuff) ?
Comment: @lain: Why not constructive? If you need an LDAP hierarchy for reasons other than serving your users, can you build it on AD or do you need a separate LDAP installation?
Answer: I worked for a large (100k+ users) environment where the AD was used to hold a significant amount of general employee information - in addition to the usual e-mail and user\department names, we also had multiple phone numbers, physical office location (down to in building office location), organisational hierarchy (who worked for whom), employee number, photo thumbnail, normal time zone, start date and a bunch of other stuff that I can't recall now.
Admittedly we had a pretty slick in house set of controlled access API's (and some authorization process to go with approving access to them) that allowed us to control delegation of rights to update specific AD properties on a per user\per group basis so it was easy to tie updates to these AD properties safely into HR apps which is where the management of this sort of data was handled.
As a user in a large organisation I found that having this sort of info available was really useful, and being able to get this sort of data via a simple LDAP query within my own apps without having to jump through hoops to gain access to HR databases was also very useful.
Answer: If you use Exchange this can be helpful by allowing people to look up others in the global address book, particularly for large organizations.  If you don't use Exchange, there's probably not a whole lot of benefit to this without some custom programming.
Having said that, as a smaller organization we used to run Exchange, still run AD, and have never put non-login information into it except full name and in a few cases department affiliation.
I should add, the biggest roadblock to this is that keeping the AD updated is a function of IT and in many organizations there's not a good process to get the kinds of information that would populate a general-purpose directory from, e.g., HR to IT -- often security or required permissions are the IT priority for new hires and updates.
Answer: We use the telephone information, organisational information (fed from our HR system) and a few extensionAttributes for misc. stuff.  The organisational information is invaluable from an IT perspective, as you can quickly see who you're dealing with, or contact teams as opposed to individuals.  The telephone information can be queried using a simple web front end.  Users have also got used to seeing quite a bit of info via Outlook.  Oh, the organisational info also gets used to dynamically populate some global groups, based on what department you're in.  These groups are then used to provide department-based access.  In short, AD is a good place to hold stuff like this.
Answer: I have seen it used in an environment to monitor when specific computers were being used as a sort of employee monitor system, but this doesn't make near as much sense as using its LDAP along with it.
We use it as a general purpose dir to work with exchange, however, we still use it with user auth for security reasons.  If it were only for inner-office staff, this wouldn't be necessary for us.

Using AD as a general purpose directory


How can I find the audio clips in a Facebook Messenger history

Question: I have a long chat history with a Facebook Messenger user.  There are a few audio clips in the history.  I don't want to scroll through 30,000 messages and clicking on audio clips.  Is there an automated or scripted solution that will allow me to easily find those links or files?
Answer: Updated answer because the question was updated.
Scroll until you find it, with a script.
Still, there isn't any nice or elegant way of doing that.
You could write a script that will scroll the conversation page until the top, and then export all the audio tags content from the page.
Another such solution, is doing pretty much the same, but on the mobile messenger view, where each time you see a block of messages and you can check the html for audio tags, and continue with the script to click on "See Older Messages...".
Anyway, you'd have to write a short script for doing that for you ¯\_(ツ)_/¯

Scroll until you find it.
Facebook messenger doesn't have a good search. It barely matches keywords, and can only show shared photos in the side panel (web view).
There isn't an option to search for shared media/files, nor any keyword I found that would match an audio clip.
You can try downloading all you Facebook information and if it really gives you all your information and conversations - dig inside the messenger conversations, and hope to find it.
Comment: Your did correctly answer the question as I asked it.  However the solution is not practical. I have edited the question to reflect that I am searching for an efficient automated way to do this.
Comment: I updated the answer, but it's still not that helpful for you, because there isn't a nice solution for that ¯\\_(ツ)_/¯   You'll have to write a script to achieve that, and I wrote some guidelines for the beginning with the hope it would be helpful
Answer: General Steps:

Download your entire Facebook data.
Navigate to the desired conversation.
Open the source of the conversation, and find all the strings that look like messages/audio/SOME_LONG_NUMBER.mp4
Those are your audio files from the conversation with the friend you chose.

In Detail:

Download your entire Facebook data.

To download a copy of your Facebook data:

Click  at the top right of any Facebook page and select Settings.
Click Download a copy of your Facebook data below your General Account Settings.
Click Start My Archive.

You'll get an email when the archive is ready for download.

Navigate to the desired conversation.

Open the archive folder you downloaded.
Open index.htm and navigate to Messages
Use the Ctrl+F to search your friend's name.
Open the conversation.

Open the source of the conversation, and find all the strings that look like messages/audio/SOME_LONG_NUMBER.mp4

Ctrl+U, or open the selected html file with some editor.
Find all the names matching *.mp4 - this will be simply achieved with some text processor and some find and replace (maybe with regex).
Save a list of all the file names.
If you want something specific and not all of them, you can search a date or phrase in the conversation page (it's a single page) and then look for your audio message.

Those are your audio files from the conversation with the friend you chose.

Take your list, and create a search phrase to match all the files in your list. For example, in windows explorer you can concatenate each name with an OR and use it to search.
Search the files under archive_location/messages/audio
Here are all your audio files! Start listening and find what you wanted!
Answer: I might be late to the party but there exists an extension for Chrome that saves Facebook chats including all the files in it.
It creates an archive with all the media present in a chat. You can also uncheck saving pictures and videos if you don't want them.
This way you can get the audio files you need.
Here's the link to the website: Messages Saver for Facebook
Answer: find the audio clip using m.facebook.com and when you click on the audio clip it will automatically download it. sadly, i don't know how to find audio clips but just to keep scrolling up. but if ever you want to stop doing that in the future just download them.
Comment: Note that the OP said he has around 30K messages and he's looking for another solution rather than just scrolling


How to get to PowerPivot data within VBA?

Question: I have my data imported to PowerPivot (based on sql query) table in my workbook. I need to copy this data to the worksheet to do some modifications. How to accomplish it with VBA?
Answer: There is no direct API but a workaround is to copy the data into the worksheet and format the data as table then create a "Linked Table" to import the data. The databases PP accesses do have APIs to access them directly from within Excel though.
Microsoft Office provides drivers that you can use to retrieve data from the following data sources:
Microsoft SQL Server Analysis Services (OLAP provider)
Microsoft Office Access
dBASE
Microsoft FoxPro
Microsoft Office Excel
Oracle
Paradox
Text file databases
http://office.microsoft.com/en-us/excel-help/use-microsoft-query-to-retrieve-external-data-HA010099664.aspx


Citizen of the UK travelling from there to Amsterdam on 11th April

Question: I am a citizen of the UK, where I live.  I am travelling to Amsterdam for a conference on April 11. The UK may leave the EU on April 12th (as a No Deal Brexit) if Theresa May's brexit deal doesn't pass. I'm travelling back from Amsterdam on April 14th. Flights, hotel and conference tickets are booked, passport is valid, etc. What preparations do I need to make to ensure that in the case of a no deal brexit, I can return to the UK on April 14th?
Comment: What is your citizenship and your visa/residency status?
Comment: Have you checked the Brexit-related travel advice on https://www.gov.uk/visit-europe-brexit ? The advice states there would be changes if you visit the EU, Iceland, Liechtenstein, Norway or Switzerland and the UK leaves the EU without a deal.  It would mean that from 12 April 2019, the rules for passports, driving, EHIC cards, pet travel and more would change. If the guidance doesn't tell you what you want to know, please edit your question to describe your specific concern(s).
Comment: @Traveller thanks I'll give that a read;
NateEldredge I'm a UK citizen
Answer: As Harper explains, you will definitely be allowed back in the the UK if you manage to get there, and the remaining EU will have absolutely no reason to launch a witch hunt for stranded Britons on short visits.
A different worry is that your flight home might be canceled if it turns out that a no-deal Brexit means that EU airlines have no legal right to serve UK airports and vice versa. If your ticket is with an UK airline, this now seems to be unlikely as the EU has passed legislation to allow UK airlines to fly to the EU for a transitional period even after a no-deal Brexit. They're poised to withdraw this quickly if the UK doesn't offer equivalent access to EU airlines, but they'd probably allow at least a few days time for the UK to fix the cock-up if things start to melt down immediately after Brexit.
I'm not aware of any positive corresponding rulemaking in the UK. This gov.uk "guidance" from 7 March states an intention to give reciprocal access, but it is not clear what would need to happen to make that a legal reality, and whether the government is on track for getting those things to happen.  It doesn't seem terribly likely that they'll choose this as the opening shot in an all-out trade war, but if your bookings are with a EU airline, you may want to start preparing mentally for possibly being stuck on the continent for several additional days before you can repatriate yourself via sea, tunnel, or a UK carrier.
Comment: The last three years has severely eroded my level of trust of politicians to organize a p*** up in a brewery, never mind an emergency transportation system.
Answer:
The EU has declared that the right of British expats are a matter for the individual member states. The Netherlands are taking measures to give temporary residence permits, so there should be no problem for visitors, either.
It is conceivable but unlikely that something could happen to air traffic. There are suggestions of temporary permits even in the absence of the Brexit deal, but these are contingent on reciprocity. There could be a tit-for-tat if things turn unfriendly.
It might be a good idea to have enough money in the bank account/credit card limit to take alternative routes home, e.g. a ferry or the train.
Comment: To buy your ticket to Harwich, in case of complete panic.
Comment: Or to get euros out of the bank before the 12th.
Comment: @Willeke, one would need pounds if one steps from the ferry in Harwich at 0-dark-30.
Comment: I see mutual non-extension of landing rights as unlikely but possible. A breakdown of the credit card system seems even less likely.
Comment: @o.m. a breakdown of the credit card system is indeed unlikely, but problems preventing transactions between the UK and the EU could be less unlikely.
Answer: Easy.  You can definitely re-enter.  One huge feature of being a citizen of country X is that you cannot be refused entry into country X.
So as a UK citizen you are entitled to enter the UK.
If you show up without papers, they can detain you until they confirm your citizenship.  However if you have proper documents along, it'll be no trouble at all.
Comment: Getting _to_ the UK border might be problematic if the UK crashes out without an air transport agreement that allows planes to keep flying. There'll still be sea crossings and the tunnel, of course.
Comment: But would the person's presence in the Netherlands be legal on the 13th and 14th?
Comment: @phoog I think *the worst-case scenario there* is they'll be in a gray area with millions of other Britons, most of them also doing short-term travel and most returning that same week; EU immigration would be disinclined to make an issue of it because they'd lack the bandwidth to do so.  *Over an issue that, once an agreement is reached, will surely give Britons **no worse** immigration deal than EU gives the USA; so Brits would already be entitled to visaless entry for 90-out-of-180 or whatever; all in all an immense nothingburger*.   Bigger fish to fry...
Comment: @HenningMakholm Or even, they could fly to Ireland and walk across the UK border going "Good Friday agreement, ha ha.."


Does a b'chor need to fast if he didn't partake in food from the siyum?

Question: If a b'chor attended (or made) a siyum on taanis bechoros but did not partake of any food does he need to fast?
Comment: Welcome to Mi Yodeya. Please note that this site makes no guarantee of validity, and does not offer professional (particularly rabbinic) advice. Treat information from this site like it came from a crowd of your friends. For a definitive ruling, please contact your rabbi. You might also want to see "[Why is it necessary to ask a rabbi?](//judaism.stackexchange.com/q/9146)" for more info. We hope to see you around!
Comment: Why do you think it would be a problem and would have to fast if he didn't partake in the meal? (Many shuls I've been in don't give any food whatsoever after the siyum. Everyone just crowds around to "hear" the siyum then leave.
Comment: http://halachipedia.com/index.php?title=Tanit_Bechorot (item 15).
Answer: The OP asks about attending the siyum and only eating later at a different place and time?
The Minchas Yitzchak (vol.9:45) and Rav Elyashav (I heard this from Rav Smith) both say (as do others) that the simchah of the siyum is what releases the fast. Therefore, you may eat later and elsewhere. One idea for this is the Gemara (Shabbos 118) that says when there was a siyum on a masechta, they would make a "yom tov". The entire day was infused with the spirit of the siyum.
Of course, since other authorities seem to require the firstborn to also partake of enough food at the siyum itself, it should be done if possible.
As to the opposite, (if the person missed the siyum, but arrived for the food only) there are poskim that say it does not help (Rav Elyashav above and others) however, according to the Minchas Yitzchak above, and others (Minchas Yitzchak (9:45); Harav M. Shternbuch in Teshuvos v'Hanhagos (1:300) quoting Harav Y.Y. Kanievsky who says that it is customary to be lenient in this matter, provided that the person is really "happy" with the siyum taking place.) It is permitted to be lenient.
Of course it is better to attend the siyum.
However, in both cases, it seems the world is lenient.
Answer: wiki
If a firstborn attending a siyum does not hear the completion of the tractate, or if he does not understand what he hears, or if he is in the shiva period of mourning and is thus forbidden from listening to the Torah material being taught, some authorities rule that subsequent eating would not qualify as a seudat mitzvah and he would therefore be forbidden to break his fast (Ben Ish Chai 1:96:25; Rabbi Shlomo Yosef Elyashiv, Siddur Pesach K'hilchaso, p. 168; Rabbi Ovadia Yosef, Chazon Ovadiah, p. 99). Other authorities allow a firstborn to break his fast under such circumstances (Minchas Yitzchak 9:45; Teshuvos V'hanhagos 1:300, 2:210 in the name of Rabbi Yaakov Yisrael Kanievsky). The Minchas Yitzchak (ibid.) suggests that a firstborn in such a position should at least try to contribute to the siyum in some way, such as by sponsoring or helping to prepare the meal.
In order to break one's fast on a seudat mitzvah, many authorities rule that one must partake of at least a kotevet of food (around 1.5 to 2 oz.) or a melo lugmav of liquid (at least around 1.7 oz.) at the seudah (Minchas Yitzchak, ibid.; Chazon Ovadiah, ibid.; Teshuvos V'hanhagos, ibid.). Other authorities rule that a firstborn need not eat anything at the siyum itself, and that he may break his fast anytime after the siyum (Siddur Pesach K'hilchaso, ibid; Rabbi Yehoshua Menachem Mendel Ehrenberg, Devar Yehoshua 2:81).
Answer: Yes, he does need to fast.
The main part of the Mitzvah is partaking of the meal. As a matter of fact, one could even eat of the meal and be a part of the Mitzvah without having heard the Siyum part.
Source: The announcement made by the Rav of the Shul I go to every year for the Siyum.
Comment: I am trusting your anonymous rav. But, to me, this still appears debatable. If and when you can, perhaps during Yom Tov, ask him to support his statement. and, perhaps, edit this, later. B"N, I shall do the same with my rav. If I'm wrong, I have no problem deleting my answer. This is a really interesting question, and I enjoyed the debate on this one.
Comment: See the piskei tshuvos who will confirm this
Comment: @DanF I'll try.  Call me old fashioned, but I don't like quoting people's names online without their permission, so anonymous rav shall remain. To be honest, the source that havarka quoted in your answer seems to read like a proof to my answer, with the exception of the last line, which one could read like you did. However, it could also be read as a continuation of the previous line, i.e. "the custom would also be to learn a bit beforehand". Also saw this http://judaism.stackexchange.com/questions/319/oops-i-just-missed-the-siyum-for-fast-of-the-firstborn?rq=1 in the related threads...
Comment: ...which quotes in one of the answers a Rabbi Strasser as saying the same as this answer (and no, he isn't the Rav of my shul). @sam Thanks, I'll try to look into that when I can.
Answer: This is an interesting question.
Many shuls in my neighborhood have no food at all. Two reasons for that:

People are hurrying to get to work on time
The shul kitchen & kiddush room, etc. is usually closed for the week, so there is no place to comfortably make a meal

The main part of the siyum is the "siyum" which means the finishing of the masechta. The meal part is called "se'udah". It is the siyum that exempts the person from fasting, not the se'udah. As a matter of fact, it is the siyum that turns the meal into a se'udat mitzvah, not the other way around.
So, technically, if someone attends the siyum, he is allowed to eat at home or wherever he wants.
Some proof to this concept, can be found in one of the paragraphs said at the end of the siyum. Rav Papa's 10 sons are mentioned because Rav Papa used to make a lavish meal at the end of completing every masechta, and he invited his 10 sons who were also great scholars. Perhaps, it was not that customary to make a meal after the siyum, and he was considered somewhat exceptional for making a bigger deal about this.
Comment: "It is the siyum that exempts the person from fasting, not the se'udah." I'm not sure that's right. In fact, I think it _is_ the meal itself.
Comment: I thought that the reason we can then eat is because we take part in the *se'udat mitzvah* -- once you've broken your fast then, it's fine to continue eating.
Comment: I learned  that you have to partake something with seuda, but now reading it again, I am not sure. Look at here

sa:470 mb:2
 ויש מקומות שנהגו הבכורים להקל ולאכול בסעודת מצוה וכן נוהגין כהיום בכמה מקומות במדינתנו להקל ולאכול אף בסעודת סיום מסכת ואף שהבכורים בעצמן לא למדו את המסכת מ"מ כיון שאצל המסיים הוא סעודת מצוה מצטרפים לסעודתו והמנהג שמתקבצים להמסיים קודם שסיים ומסיים לפניהם המסכת ושומעים ומצטרפים עמו בסיומו ואח"כ עושין סעודה

http://he.wikisource.org/wiki/%D7%9E%D7%A9%D7%A0%D7%94_%D7%91%D7%A8%D7%95%D7%A8%D7%94_%D7%A2%D7%9C_%D7%90%D7%95%D7%A8%D7%97_%D7%97%D7%99%D7%99%D7%9D_%D7%AA%D7%A2
Comment: @Scimonster I don't think this is how it works. Although, now that you mention it, this morning, my Rav did say that if there were a brit, you would not need to make a siyum! So, I'm uncertain, myself. Is it the meal or is it the event? I believe it's the event. My reasoning - the brit does not require a se'udah (proof? You can have a brit on Yom Kippur)
Comment: @havarka - good source. But read a bit more carefully, esp. near the end - והמנהג שמתקבצים להמסיים קודם שסיים ומסיים לפניהם המסכת ושומעים ומצטרפים עמו בסיומו . It seems that the main part is to join in the siyum. I understand, in a sense that the following words, ואח"כ עושין סעודה is "incidental". I.e. the siyum is the *reason* for the se'udah, not that the se'udah is a requirement. Hence, attending the siyum is what allows one to break the fast. Likewise, attending a brit, and possibly a Bar Mitzvah (Have to investigate this) would allow one to break the fast.


Justifiable violence in Buddhism?

Question: Does Buddhism preach absolute non-violence? Or is there any instance where Buddha had thought that violence can become a necessity under certain situations?
Comment: See also [Can or should a Buddhist defend themselves physically](https://buddhism.stackexchange.com/questions/2071/can-or-should-a-buddhist-defend-themselves-physically)
Answer: No, householder Somanna, the Buddha and all wise approve that one thing should be killed, and only that:
Having killed what
    do you sleep in ease?
Having killed what
    do you not grieve?
Of the slaying
of what one thing
    does Gotama approve?
[The Buddha:]
Having killed anger
    you sleep in ease.
Having killed anger
    you do not grieve.
The noble ones praise
the slaying of anger
    — with its honeyed crest
    & poison root —
for having killed it
    you do not grieve.
Ghatva Sutta
Without need to have any doubt, if hearing or seeing that someone approves harming, encourages to such by signs and words or even performing such, that such person is not even near related to the Buddha, wise and their following, but harmful thieves in this world.
Those who have doubts, regard them as not having found refuge in the tripple Gems jet, how much ever they use the Gems, even tell that they are Buddhist, knowing, and follower.
May one be careful and blessed to never assosiate with fools and bad friend.
As already quoted, not all are capable in getting the message.
The Simile of the Saw, is possible the most famous collection on it.
Not for any purpose:

"What do you think Dhanañjani? There is the case where a certain person, for the sake of his mother & father...for the sake of his wife & children ... his slaves & workers ... his friends & companions ... his kinsmen & relatives ... his guests ... his departed ancestors ... the devatas ... the king, ...There is the case where a certain person, for the sake of refreshing & nourishing his body,..., does what is unrighteous, does what is discordant. Then, because of his unrighteous, discordant behavior, hell-wardens drag him off to hell. Would he gain anything by saying, 'I did what is unrighteous, what is discordant, for the sake of my mother & father. Don't [throw] me into hell, hell-wardens!' Or would his mother & father gain anything for him by saying, 'He did what is unrighteous, what is discordant, for our sake. Don't [throw] him into hell, hell-wardens!'?"
"No, master Sariputta. Even right while he was wailing, they'd cast him into hell."...

Harmlessness is one of the three factors of right effort,following right view.
What ever might appear as harmfull, like rebuking fools, there by the words, right speech,  of compassion ends what ever conductive support can be given for one who acts (by thought, words and speech) for his longtime disadvantage.
(Note: this is not given for trade, exchange, stacks or entertainment, but only as means to escape this binding wheel)
Answer: The Buddha generally taught the Buddhist Path rather than a formula for all of society. For example, in many of his teachings, he said those who break the law get executed by the King. The Buddha never taught the King was wrong for executing criminals. For example:

'This person has murdered a man or a woman.' Then the kings have them
arrested for killing, and execute, imprison, or banish them, or do
what the case requires.
AN 5.178

While it is unlikely the Buddha actually taught DN 26, DN 26 says:

But sire, what are the noble duties of a wheel-turning monarch?'
'Well then, my dear, relying only on principle—honoring, respecting,
and venerating principle, having principle as your flag, banner, and
authority— provide just protection and security for your court,
troops, aristocrats, vassals, brahmins and householders, people of
town and country, ascetics and brahmins, beasts and birds.

Buddhism generally makes a distinction between itself & the rest of society. Buddhists should do their very best to refrain from violence.
Answer: It's hard to "prove a negative" e.g. to prove that someone never said something (e.g. that violence is necessary).
One way to try to do that is to quote an expert on the subject.
In Getting the Message, Thanissaro Bhikkhu wrote,

When asked if there was anything whose killing he approved of, the Buddha answered that there was only one thing: anger. In no recorded instance did he approve of killing any living being at all. When one of his monks went to an executioner and told the man to kill his victims compassionately, with one blow, rather than torturing them, the Buddha expelled the monk from the Sangha, on the grounds that even the recommendation to kill compassionately is still a recommendation to kill — something he would never condone.

The next sentence of that quote is,

If a monk was physically attacked, the Buddha allowed him to strike back in self-defense, but never with the intention to kill.

I think that latter means "if trapped, to strike a blow, desiring freedom".
So I guess that's a limited, perhaps a harmless, violence.
Answer: The way I understand what Buddha taught was a set of natural law, not a man-made law. (except for Vinaya perhaps)
What Buddha taught was Kamma and Vipaka.
Angulimala killed many people but still became an Arahant.

Justifiable violence in Buddhism?


Modify dash minimize/maximize/close icons

Question: I'd like to be able to customize the dash minimize/maximize/close icons, specifically to be able to change the color.
I've tried several custom gtk+ and window themes (using gnome-tweak-tool), some include new dash icons but I can't seem to locate the specific icon files to replace for setting my own icons.
Default theme 'Ambiance' files /usr/share/themes/Ambiance/unity/close*.png would appear the files that need to be replaced, however replacing them does not change the dash icons.
If not possible, I'd settle for being able to remove them completely.
Anyone had any experience with this?
Answer: The Dash icons are in <code>/usr/share/unity/5/</code>
I've only re-colored the 3 close .png's to match what I use elsewhere


how to apply nginx rewrite from htaccess

Question: I installed ispconfig/nginx on ubuntu 12.10 following "perfect server" here:
http://www.howtoforge.com/forums/showthread.php?t=61141
I need to apply rewrite rules to nginx from a .haccess file with these contents:
RewriteRule ^(.)/(.)-video_(.*).html$ musicvideo.php?vid=$3
RewriteRule ^([^/])-video_(.).html$ watch.php?vid=$2
i used an online converter and got this output:
location / {
rewrite ^/(.*)/(.*)-video_(.*).html$ /musicvideo.php?vid=$3;

rewrite ^/([^/]*)-video_(.*).html$ /watch.php?vid=$2;
}

Then I put the code in ./sites-available/default under server block and restarted nginx but I am getting error:
duplicate location "/" in /etc/nginx/sites-enabled/default:133
nginx: configuration file /etc/nginx/nginx.conf test failed

and If I put my rewrite rules within the existing Location:
location / {
            # First attempt to serve request as file, then
            # as directory, then fall back to displaying a 404.
            try_files $uri $uri/ /index.html;
            # Uncomment to enable naxsi on this location
            # include /etc/nginx/naxsi.rules
rewrite ^/(.*)/(.*)-video_(.*).html$ /musicvideo.php?vid=$3;

rewrite ^/([^/]*)-video_(.*).html$ /watch.php?vid=$2;
}

then nothing happens! could someone please point out to me what I am doing wrong?
Answer: The order of directives matters in nginx.  Try moving the rewrite rules up to the top of the / location.


Normal to have API error while saving a Case Type?

Question: I'm on CiviCRM 4.6.18 and Drupal. When I save a case type, I keep getting an error on the top right that says "API error: DB Error: already exists." I'm not sure if this is causing another issue I'm having which is when I create a case, the loading keeps hanging.
Answer: No, not normal. And not, AFAIK a known error. In order to make sense of something like this devs usually need debugging information. There is error output in the log files in the ConfigAndLog directory - on drupal sites this will usually be in sites/default/files/civicrm/ConfigAndLog
Answer: Not sure what was going on, but thank you to Eileen. I did the following steps on CiviCRM 4.7.18, probably not ideal if you already have data though.

Delete all cases and case types.
Delete all relationships
Disable CiviCase
Clear Cache
Re-enable CiviCase


Ideas to promote more questions

Question: What are some ideas that the community has that can promote more questions?  Our new questions per day rate is awfully low.  What can we do to encourage growth?  The recent attempt at a theme week failed - other ideas?
Answer: I've started a separate meta thread to talk about the possibility of an SE-funded photography gear lending program to give you guys new material to ask questions about. Please weigh in over there if you're interested.
We at SE are working on a tool that will hopefully bridge main site activity with meta activity better, so don't shy away from initiatives that make use of meta. This feature will hopefully be coming soon; I will keep you updated.
I have been trying to get in touch with medium- to largely famous photographers to work out some kind of partnership/mutual promotion, but many of the big names are either too busy or otherwise unresponsive to my attempts so far. If anyone has any personal connections, definitely leverage them - promote this site to your photographer friends yourself, or you can always let me know (in chat or via email - listed in my profile) who you think would be a great addition to and advocate of the Photo.SE community.
Comment: How about trying to involve local photo shops. Here in Oslo we have one big shop where most of the enthusiasts and pro goes, and that's probably true for other cities too. It might be a way to inform more photographers about the site.
Answer: It might help to take a look at the F.A.Q. and offer more suggestions on the sorts of questions that are appropriate.
-
I realize photo critiques were voted as off topic, but would it be possible to add some kind of section for them? This could encourage community involvement.
-
Things like the weekly photo contest are great for keeping people involved on the site. What about weekly assignments or projects? Something like a subject that people should try to photograph as a second contest next to the weekly photo one, or instead of it.
This would also make people get out and take photos if there was a (obviously unenforceable) rule that photos for assignments have to be taken during the week they are put in for.
-
Promoting the site is also an option. I bet 99.some% of the world's photographers have never even heard of StackExchange, but many would love to visit and ask questions on the site, if there was some kind of easy to follow guide on how the site works. Since not everyone is a tech geek, and they might feel intimidated perhaps some kind of blog post that was shared around photographic communities would help.
Comment: I think the difference between an theme and an assignment is notable; one is meant to teach while the other is more of a showcase. Also the former is less intimidating to new uesrs, I think.
Comment: These are good community ideas - do we think they'd turn into questions on the main site?
Comment: @The 'assignment' part is basically out themes that we're starting to do on the PotW.  There's a theme starting on March 5, check the comments in this week's PotW
Answer: Analyse the data.   How many questions per week per active user do we get compared to other stackexchange sites?    If it's high or average, then we just need more visitors.  If it's low, then perhaps people are more satisfied just to browse, or they browse and decide not to linger.
Answer: getting new members/questions - we need more promotion, as Bob said. Many of us probably are active on other sites and can put up a thread about this site. Anyone who knows bloggers and such can ask them to mention us.
From within the community - I think the theme was a good idea.  Once you see questions about X, it triggers other questions you might have.  Not sure why it didn't work - I think mainly because meta doesn't get much visibility (this thread has 24 views).
I think it would snowball if we got to a decent rate.  If there were 3 pages of new questions each day, people would spend more time.  When it hardly ticks over, people tune out.  Possibly if a core group of people make a concerted effort to create new questions it will prime the pump, so to speak.
I've seen SE results high up in search engines, I don't know if there's any optimisation we could do there (tags or otherwise) that would drive more traffic.  I suspect it's pretty good already.
I would like to see more professional photographers on the site.  There are a few, but most of us seem to be hobbyist.  Or even get some rock stars like David Hobby or Joe McNally to hop on and answer some questions (on main page or meta or chat).
Comment: @Laura is working on a few of those things - she tries to actively reach out on the net.

Ideas to promote more questions


Sleeping bags: Tzitzit and Shatnez

Question: Would a sleeping bag need tzitzit because you get inside of it, making it kind of a garment? What about shatnez? Since you get into the sleeping bag like a type of garment, does it need to not be wool and linen mixed together?
Comment: Do sleeping bags have four corners?
Comment: In my humble opinion it is not a stop stupid question
Comment: I can't see how Shaatnez wouldn't be a problem
Comment: @DoubleAA - Yes they do. (NOT THE MUMMY STYLE ONES, just the normal warm weather ones.)
Answer: Well to address the Tzitzis questions the Mechaber writes in Orach Chayim (18:2)
(Sources provided from Sefaria)

סְדִינִים, אַף עַל פִּי שֶׁאָדָם יָשֵׁן בָּהֶם בַּבֹּקֶר, אֵין מְטִילִים בָּהֶם צִיצִית.
Bedsheets, even though one sleeps in them in the morning, should not have tzitzis attached.

The Magen Avraham (see over there) brings down that there opinions that differ upon this idea and recommends that one should round one of the corners of the sheet so as to not obligate it in tzitzis according to everyone.
Hope this helps (partially) .
Comment: B''H thank you does help for the tzitzis part. :) Thank you.
Answer:
Would a sleeping bag (th warm weather ones) need tzitzit because you get inside of it, making it kind of a garment?

A sleeping of this type of sleeping bad has no four corners. warm
weather sleeping bag
Despite the rectangular aspect it is as a flattened cylinder
(despite the possibility to open it with the zipper, the use is when
the zipper is closed).
But even a rectangular blanket or bed sheet, are exempted from the
requirement of tzitzit. because they are night garments (as
mentioned by @Ploni Almoni from SA). See Menachot 43a:

It was taught: That ye may look upon it: this excludes a night
  garment.

What about shaatnez? Since you get into the sleeping bag like a type of garment, does it need to not be wool and linen mixed together?

See Mishna Kil'ayim, 9, 2,:

הַכָּרִים וְהַכְּסָתוֹת אֵין בָּהֶם מִשּׁוּם כִּלְאַיִם,
  On the first glance, the Mishna seems to permit:
  Cushions and blankets has no problem of Kil'aym. But Bartenura explains the real meaning of this statement:
לְפִי שֶׁהֵן
  עֲשׂוּיִין לִשְׁכִיבָה, וְהַתּוֹרָה אָמְרָה (וַיִּקְרָא יט) לֹא
  יַעֲלֶה עָלֶיךָ, אֲבָל אַתָּה מֻתָּר לְהַצִּיעוֹ תַּחְתֶּיךָ. וְהַנֵּי
  מִילֵי כְּשֶׁהֵן קָשִׁים וְרֵקָנִים וּנְתוּנִים עַל גַּבֵּי
  אִצְטַבָּא,

They are hard and not convex.  He adds they don't touch the skin, so cannot wrap by a thread a small part of the body.
__In summary the sleeping bad cover the body on top and on bottom,  is flexible and concave,  and sometimes touch the skin.  Each of these details is sufficient to make it susceptible to be prohibited by shaatnez
Comment: @Ezra Hoerster thanks to you for the serie of questions about tztzis which cover a great spectrum of halachot

Sleeping bags: Tzitzit and Shatnez


Why did Thanos plan the Chitauri invasion when he only needed Tesseract?

Question: In the Avengers movie, Loki got the Tesseract from S.H.I.E.L.D., which he then used to open the portal. Since Thanos' primary objective was to obtain the Tesseract, which Loki already had and could have used to transport himself back to Thanos, what was the point of the Chitauri invasion after accomplishing that?
Comment: "The primary objective of Thanos was to obtain Tesseract." Was it? When was that stated?
Comment: @PaulD.Waite That was the whole point of movie. That's why Tesseract was taken away from the Earth in the end. See transcripts from the accepted answer.
Comment: @SachinShekhar: ah yes, gotcha.
Answer: Thanos and Loki had an agreement in which 2 things were covered.

Loki would retrieve and hand over the Tesseract to Thanos.
Thanos would supply his Chitauri army to Loki, so that Loki could conquer Midgard.

The Chitauri invasion was Loki's idea, not Thanos's. It was Loki's intention to conquer Earth. Thanos was in it only for the Tesseract. This is evident from several points in the story line.
In the very beginning, the voice-over says

'The world will be his. The universe yours."

In another conversation,

LOKI - don't threaten, but until I open the doors, until your force is
  mine to command, you are but words.
  THE OTHER - You will have your war, Asgardian. If you fail, if the Tesseract is kept from us, there will be no realm, no barren moon, no crevice where he can't find you.

This conversation highlights that "The Other" who is Thanos's handyman, clearly identifies that Thanos is in this only for the Tesseract.
Also note the usage of the words "Your war". This clearly shows that the invasion was Loki's idea, and not Thanos's.
Answer: It's similar to Thanos' deal with Ronan in Guardians of the Galaxy.

Thanos: Get me the orb and I'll destroy Xandar for you.

Once Ronan realized the orb contained an Infinity Stone, he double crossed Thanos because he could just use it to destroy Xandar himself.
He also might have been aware of Thanos' kill half policy and Ronan wanted them all dead.
Answer: This was the payment to Loki.
Thanos agreed with Loki that Thanos will get the Tessarct and Loki the ruling over Midgard.
Answer: Earth also held the time stone as well as the portal to the aether appearing on Earth during the time of the realms colliding. If Thanos knew either of these things the invasion would have been worth it.
Comment: Is there anything that suggest Thanos knew of these things? Or the writers/producers had even thought of the existence of the time stone/aether?


What cost-effective things can I do to help my knives stay sharp longer?

Question: I'm a poor college student that doesn't know much about his knives, pots, and pans. Specifically is there anything that I can do to make my knives stay sharp longer and maintain them without spending too much money?
Comment: That's a very broad question, too broad to answer in one response.  Could you please split it into several questions, or make it more specific?  Otherwise it will probably be closed.
Comment: Agree -- too general.
Comment: I think he's asking about the most cost effective way to maintain reasonable sharpness on his knives. So I assume for example, buying better knives and paying someone to sharpen it regularly is out of the question. @And0r4k, if this is the case make an edit and take out your "etc".
Answer: Here are a few rules I follow with my own knives.

Don't put your knives in the dishwasher. Hand wash and dry immediately after use.
Store knives where they won't be banging up against other hard things: my favorite is in a wooden knife block.
If you must store your knives in a drawer, protect the edge. You can use a commercial solution like this guy, or cardboard and tape if you're on a shoestring budget.
Don't cut on a glass cutting board. They look nice, but will dull your edge.
Get a steel and use it. A steel is not for sharpening, but for maintaining a sharp edge. Honing with a steel before each use will help keep the edge straight and sharp.
Don't use dull knives. Either learn to sharpen yourself, or have them professionally sharpened.

Slightly off topic, but if you're a starving college student who wants to have a high-quality knife or two at a very reasonable price, take a look at Forschner/Victorinox.  Yes, the Swiss Army Knife people. I was turned on to them by professional chefs, and have found them every bit as high-quality as my much-more-expensive Henckels and Wustof-Trident knives.
Comment: I'll also add that bamboo cutting boards seem to increase wear-and-tear on knife edges, so probably worth sticking to regular hardwood or soft plastic. +1 on the Victrinox knives.
Comment: I'll second the Forshner chef's knife -- I've had one for a few years and it's fantastic (only had to get it sharpened once). Don't buy those cheap knife sets they sell at warehouse stores -- they'll go horribly dull in months, if not weeks.
Comment: +1 for hitting all the good 'points' (hahaha).  I can say from experience that Victorinox knives rock. I was given a Chef knife and a pairing knife in 1991 when I was just starting out in the kitchen. Still have them and still use them on a regular basis. Ya, they're not as thick as Trident/Henckels but once sharpened were like a razor. Also, buy yourself a sharpening stone and learn to use it. Saves you lots of money i the long run. PLus its very Zen.
Comment: I hate wooden knife blocks because they are a microbe store. I don't like cardboard because it harbours mould spores. If you want to protect the edge on a knife, use the plastic edging they sell in DIY stores, or the "slide binders" sold in stationery places for holding papers together - both are a lot easier to sanitize than any alternatives.
Comment: +1, glass cutting boards dull any edge in no time and so do ceramic boards
Answer: Timber boards and learn to soak in boiling water and soap in the sink.
Or get some "decent" plastic ones
Unless cutting meat. wash KNIVES with cold water. By hand. then dry and store in prev protections to suit.
Sharpening.
Buy a reasonable WETSTONE  $20 will find a usable Basic Fine\Coarse one.
Soak in a dish of water for 15min's b4 use. I sit it between the two sinks in kitchen at home and run cold tap on it while using.
When knife to your edge. dry it. Then start with a decent Diamond Steel.
 I just bought a reasonable quality one from Mitchel Manufacturing. (They make Butchers tools for the meatworks trade.)
600 grit. Works well after you rubbed the spare dust off. And they're CHEAP.
Then I use either an old SMOOTH  diamond steel or a smooth Steel Steel. Followed by a strop.
Mine is a Mules saddle strap from army disposals. around 5 ft long. 3in wide. Thick with big brass buckle.
It made two nice strops.
Depending on the knife. you'll need to stone every several months. Steel regularly but not too much. and I strop every time b4 use.
if you want good quality. fairly cheap that will last your lifetime. Get some Mundial
 I bought missus a 15mm Cooks and a 15mm Utility. Both nice Well balanced and HOLD a good edge.
I have Wusthof (40 yrs) and recently bought a new Utility, after 40 odd yrs I'd worn\stoned the blade down to it's thickness. Sharp but you have to work at it.
I splashed out on a Torijo DP3 Utility, Laminated.  (spoiled myself a little)
It's my favourite general knife and LOOKS  "lovely.Plus"
A pleasure to use.
But you'll never NEED to go past the Mundial for general cooks work.
They as good as most others, Apart from Japanese..
Those skinny pressed blades can be sharp. but for a nice feeling knife that you LIKE to use go a bit better. You only buy it once. and DOES become an extension
Buy a 15\20cm Cooks. Mundial?  that'll do 90%of your work. ANY Paring knife from supermarket. Then a  Utility. Mundial?.
Unless cutting seriously I use those two blades for everything.
Bread Knife. I have 2 in the drawer.
I prefer a 13in meatworks butchers knife For Pumpkin Cabbage etc. Long enuff to control at both ends while using. (Safer) And a 6in Curved Boner from same place (Swibo. HARD steel)
Pricks to sharpen but hold it when you get there.
Meatworks knives will cover all you want. Crude but good steel. Cheap as. and do a good job.
They designed to do a ten hr shift, continuously. Just Another way to go when your pocket light.
king of knives sell them and are closing down.
Comment: Although I learned to use a whetstone decades ago, I'm surprised you're recommending it 'every several months' for someone who's a college student.  Professionals might need to sharpen more often, but a home chef can probably get a year or two between sharpenings if they treat their knifes right.  (and a bad sharpening will ruin your knives)


Why are my football action shots blurry?

Question: I am shooting with a Nikon D5200 using a 55-200mm lens to take photos of a high school football game.  I'm using the sports setting but unsure what my other settings should be.  Can you please help?   Thank you in advance!
Comment: Please add example photos to your question and also add the camera settings you were using (shutter speed, ISO, aperture) that you can find in the EXIF data of the image file.
Answer: There are three basic issues that can make sports pictures blurry:

Subject motion too fast for the selected shutter speed.
Missed focus
Too much camera movement for the selected shutter speed.

The camera's "Sports" setting can only do so much to help you. The amount of light available and the lens you are using don't give it as much to work with as what it needs.
The basic problem is the "slow" maximum aperture of the lens you are using when it is zoomed all the way in to 200mm. At f/5.6 there is 1/2 as much light getting through your lens to the sensor as there would be at f/4, and 1/4 as much light as there would be at f/2.8. That means for the same ISO you need a shutter time twice as long as you would at f/4 and four times as long as you would at f/2.8. If your D5200 allows you to select ISO while in Sports mode then you need to increase it until you are getting shutter times of at least 1/250 second or shorter. 1/500 second is even better and 1/1000 second is minimum most pros try to use with football at night. But to get that you're going to need a much faster lens.
I shoot high school football regularly at night under reasonably good light for a high school stadium. I use Manual exposure mode, f/2.8, and 1/800 second at ISO 2500.
The camera I use also times the release of the shutter with the peak of the flicker caused by the lighting that fluctuates with the frequency of the alternating current that powers the lights. Without a camera with that feature I'd be forced to use about 1/500 second with ISO 2500 and f/2.8 and some of my shots would still be underexposed while others would be overexposed depending on whether the lights were peaking or in the trough of the alternating current. Worse, many frames would be exposed dimmer (and browner in color) on one side of the frame and brighter (and bluer/whiter) on the other.
Without a flicker reduction feature and when using a lens with a maximum aperture of f/5.6 the best you could do in the same light would be somewhere around ISO 6400, f/5.6, and 1/250 second. At ISO 6400 with a camera using an APS-C sized sensor the noise in the photos and/or the resulting loss of detail caused by application of noise reduction is going to rob your photos of a lot of detail and the ability to display them at relatively large sizes.

Canon 7D Mark II with EF 70-200mm f/2.8 L IS II @ 185mm, ISO 2500, f/2.8, 1/640 second.

Canon 7D Mark II with EF 70-200mm f/2.8 L IS II @ 185mm, ISO 2500, f/2.8, 1/800 second.
Even at 1/800 you'll get some blurring of the fastest parts of the fastest players. Notice the foot of the ball carrier as he breaks free of the defenders with a burst of speed.

Canon 7D Mark II with EF 70-200mm f/2.8 L IS II @ 185mm, ISO 2500, f/2.8, 1/800 second.
Comment: Question and comment. Noticed that all the images are at 185mm. Is that coincidence or do you deliberately hold back from the full 200mm length in the lens?  Also, information on the frequency at which you capture action shots at this level of quality relative to the number of photos shot might add useful context regarding how hard night sports are.
Comment: @benrudgers More or less just a coincidence that I didn't even notice. A lot of times I might start at 200mm and as the play develops (and gets less predictable) I'll pull out a bit, especially if the play is moving towards the shooting position. Since I don't need to push images for immediate publication I have the luxury of framing a little wider and then cropping any extraneous items around the edges of the frame. All three of these were probably cropped to one degree or another.
Comment: @benrudgers Night sports *are* hard. They push both the equipment and the photographer to their absolute limits. But when it comes to getting shots like this to a customer they don't care if you had to take 10 frames or 10,000 frames to deliver three images with the quality they want. I know guys that still shoot like they've got film in their cameras and I know guys who shoot 10-12 fps every play. Most of us are somewhere in between. It also helps to know your gear. When using an APS-C body I tend to shoot more frames because the AF will never be as consistent as a same generation FF body.
Comment: I often get multiple frames of a developing play, most or all of which would be usable in their own right, and select the one I like the best for delivery/publication. Sometimes I get outstanding shots that I can't use because it shows a player for the team I am covering getting waxed by a player on the other team. But the fact remains if you need f/2.8 to get to 1/800 second at ISO 2500 you're not going to get any of those shots with an f/5.6 lens. You *might* get a few usable shots at 1/200 second where the motion blur away from the face/torso is acceptable.
Comment: For more regarding keeper rates, please see: http://photo.stackexchange.com/a/71354/15871
Answer: There are two sources of blurriness:

Motion blur caused by too slow a shutter speed; and
Blur caused by camera shake.

Without a sample photo we can't tell which you've got. If you don't understand the basics of exposure, your shutter speed may be too low; and if you're using a long lens and haven't acquired a steady hand through practice, motion blur is possible.
In general, to stop action you need a high shutter speed. Go out this afternoon and shoot cars on any nearby road using a variety of shutter speeds till you get the hang of it. Also you should read some tutorials on basic exposure. Everyone needs to know the fundamentals of shutter speed, f-stop, and ISO.
To hand-hold a long lens, you need to learn to use your hands and body to create a stable platform for your camera; then practice a lot.
Comment: Blur could also come from missed focus
Comment: @dav1dsm1th That too.
Answer: Sports setting should use the fastest aperture available.  I would suggest raise ISO or use auto ISO.
Comment: the fastest _aperture_ available?


Declination of the Sun formula

Question: I encountered a book discussion that defines the Sun's declination as 23.5 degrees (inclination of Earth's equator to the ecliptic) times the sine of the Sun's longitude. Does this make sense? How do i visualize it?
Answer: Yes, it is correct. For better precision:
Declination =23.5*sin(longitude)
This is true only if you don't take into account the eccentricity of Earth's orbit and other movement. It isn't easy to understand why, but I'll try ti explain it.
The different declination of the sun during the year is generated by the different angle of inclination of the Earth (the north pole point always in the same direction, so during the earth revolution the poles don't point always in the sun direction and the protection of the inclination on the sun-earth plane change during the year)
So, what wee see of the sun is the projection of the circular movement of the earth on a line of sight, so an harmonic motion.
Comment: Why is this a community wiki answer?
Answer: Yes, see graph.
At the March equinox, the Sun's ecliptic longitude $\lambda_\odot$ is zero, and the Sun's declination $\delta_\odot$ is zero and increasing.
At the June solstice, $\lambda_\odot$ is 90$^\circ$ and $\delta_\odot$ is at a maximum, 23.5$^\circ$ north of the equator.
At the September equinox, $\lambda_\odot$ is 180$^\circ$ and $\delta_\odot$ is zero and decreasing.
At the December solstice, $\lambda_\odot$ is 270$^\circ$ and $\delta_\odot$ is at a minimum of -23.5$^\circ$.

Declination of the Sun formula