How to simulate a parallel computer (with certain number of processors) on a serial computer

Question: I am a novice to parallel computing. I would like to solve the traveling salesman problem (TSP) using a parallel genetic algorithm (GA). I need to write a simulator of a parallel computer (for example, a multicore workstation) that will implement the parallel version of the GA. But the simulator should run on a serial processor. I know the basics of GAs and I know how to design a GA algorithm to solve the TSP. I thought that this could be an example of an "embarassingly parallel" problem in the sense that I could assign each processor a fixed number of chromosomes (i. e, potential solutions, with solution meaning a given sequence of cities to be visited as specified by the chromosome) with the task of calculating the objective function for each of the assigned chromosomes. In this case, the objective function for a given chromosome is the inverse of the total distance described by that chromosome. The task of performing crossover and mutation would be carried out by a master processor. If this is a valid or reasonable way of parallelizing the problem, then there's no need for inter-processor communication during the objective function evaluation step and I can hardly see this as a truly parallel problem. Since minimum communication is needed, wouldn't the speed scale with the number of processors? What would we learn from such a simulation that we don't already know? I'll be grateful for any thoughtful answers.
Comment: Just run the parallel program(s) on a system with one processor. The operating system will take care of the rest.
Comment: There is no speedup if you emulate a parallel computer with a serial one of course. What's the end goal?
Comment: What are your goals?  You can learn things from any product you create, but unless we understand what kind of things you're trying to learn, it's hard to create an answer.  It sounds like you're saying "This is a problem which is uninteresting from a parallel computing perspective, but can it be interesting to make a serial version of this uninteresting parallel computing problem?"
Comment: Speedup is not the end goal here. It is simply to simulate a parallel computing platform on a serial computer. Are there free, easy-to-use simulators/emulators of a parallel computer that let you run a parallel program on a variable number of processors?
Comment: I'm not sure I understand the problem, but most APIs / frameworks that allow you to harness multiple cores don't care how many you actually have. For example, assigning a task queue to a thread pool ( https://en.wikipedia.org/wiki/Thread_pool ) it doesn't matter how many threads you have (and the threads be run by multiple processors)

More generally, you could write an algorithm in terms of some "Parallelizable" interface with functions like "map", etc, and those functions could have sequential or parallel implementations.
Answer: The Traveling Salesman Problem (TSP) is a classic problem because it's hard to deterministically solve in a decent time frame, classified as NP-hard.  Genetic algorithms can get a good solution more quickly than NP-hard time, but there's no guarantee that you'll find an actual optimal solution.  This can be a good trade-off if you're programming, say, a driving-direction app, but it doesn't get around the NP-hard issue since it doesn't reliably solve the actual NP-hard problem.
Note that genetic algorithms are stochastic (probabilistic).  It's entirely possible that you could guess the exact best solution on the first go, or that you'd never guess it after a billion years.

I would like to solve the traveling salesman problem (TSP) using a parallel genetic algorithm (GA). I need to write a simulator of a parallel computer (for example, a multicore workstation) that will implement the parallel version of the GA. But the simulator should run on a serial processor.

As others have said, this will cause your program to run slower than if you hadn't split it up.  Parallel solution techniques are inefficient compared to single-threaded solution techniques; the only reason that we use them is to leverage additional processors.  If you don't actually take advantage of additional processors, you pay the cost for it without enjoying the benefit.
That said, almost all modern computers have multiple cores, even cell phones and tablets.  In the paragraph above, "processor" refers to a processing unit, which single CPU's have multiple instances of.  Your computer probably has at least 2 if it's a laptop or 4 if it's a desktop.
Also, note that processors often claim to have twice as many "logical cores".  When doing numerical problems, you mostly just care about physical cores; ignore the additional logical cores.  With Intel processors, this means ignore Hyper-Threading.  With AMD processors, this often means dividing their claimed count by two, since I think that they share floating-point units (FPU) between cores.  Those extra logical cores are useful in common computer tasks where there are thread waits and such, but they're usually harmful in scientific computing.

Since minimum communication is needed, wouldn't the speed scale with the number of processors?

Ideally, if you get 100% parallelization efficiency, total speed is equal to the speed of each of the individual processors working individually, combined.  Lots of things detract from that ideal, including communication time.
As much as possible, you want to split the problem up into large chunks that a processor can focus on, then combine those chunks at the end, or at least infrequently.
Too much communication will actually make a bunch of processors working together slower than a single one working alone.  For example, consider
return a + b + c + d;  // Single-threaded calculation

If you split this up into
half1 = worker1.Add(a, b);
half2 = worker2.Add(c, d);
return half1 + half2;

, your program will run much slower than in the first case, despite using multiple cores.  The problem is even calling other threads costs far more than simply adding the numbers together, so you've slowed the program down by a huge factor as soon as you do the first worker call.
The trick to remember is that you want to call workers only when you have a lot of work for them to do while the current thread does a lot of work itself.  If that doesn't hold, then it's more efficient to just do the work in the current thread.

What would we learn from such a simulation that we don't already know?

Nothing, really.  This is a common homework problem in many college classes on optimization, so it's been done hundreds of thousands of times before.  I'm assuming that this is part of one of your homework problem sets.
Conclusion
If you're in college, you may have access to a good version of Visual Studio through Microsoft Imagine (previously called DreamSpark).  If not, you can download Visual Studio 2015 Community (noting that 2017's in RC right now).
If you use C# in Visual Studio, it should be pretty straightforward to create your parallel genetic algorithm optimizer for the traveling salesman problem.  Since your PC's probably already multi-core, you can take advantage of the speed up from it.  But, even if it's not multi-core, you can still do multi-threaded runs, and the OS will interleave the threads to simulate a multi-core process.
Answer: I'll have to make some assumptions here. It seems you have a problem where some amount of work X could be distributed on practically any number of processors, while some other work Y needs to run on one processor only. And you have a single processor and want information about the behavior on n processors.
You don't really have to simulate a system with n processors. And if you could, the thing that you cannot simulate is the time behaviour. But all you really have to do is measure the time that each task takes, figure out dependencies (where one task cannot continue running until another task has finished), and you should be able to figure out all you want.
Answer: At the following paper [1] they are talking about some cloud simulators, and comparing them with a Raspberry Pi cluster. Basically they are saying that a Raspberry Pi cluster is the cheapest way to have a system with more than 1 CPU. They also saying that cloud simulators are not reflecting to the real network traffic.
So, regarding your question, even if you have a simulator you will not even get close to a cluster machine.
I would suggest you at first, to try threaded parallelism, and if you believe that is worth it, you can buy time at a bigger machine, and work with process parallelism. You can also try process parallelism on multi-core CPUs and then move to a bigger machine.
[1] Fung P.T., White D.R., Jouet S., Singer J., Pezaros D.P., "The Glasgow Raspberry Pi Cloud: A Scale Model for Cloud Computing Infrastructures," icdcsw, pp.108-112, 2013 IEEE 33rd International Conference on Distributed Computing Systems Workshops (ICDCSW), 2013
PS: Can you post the algorithm your going to use?
Comment: Parallel != distributed.
Comment: -1.  This is very bad advice because almost all computers today, including cell phones, have multi-core processors.  It'd be surprising if the OP's computer isn't multi-core.
Comment: Also, I'd add that desktop CPU's tend to be much faster than Raspberry Pi's.  Unless you bought lots of them, a desktop-based emulator should be faster, not to mention a lot easier to work with, plus it wouldn't cost all that money and time to assemble the cluster.  Don't get me wrong, Pi clusters are neat, but they're not practical for the OP's interest here.


Portable power for an UNO with a nrf24l01+ attached?

Question: Okay so I have an UNO that has an nrf24l01+ attached. I want it to be completely wireless so free of the 5v USB power and the 12V wall plug. In this case what can I use? I do not wish to plug the power directly into the Vin as I am relatively new and afraid that it might fry the board. So I wish to plug it into the barrel jack. So I have read that using a 9v battery to power UNO is a waste of power as most of the power is translated into heat. Also, using 4 AA batteries seem to be a good solution except that I'm not sure if it has enough power for nrf24l01+ as I've read that an arduino with nrf24l01+ on batteries creates an unstable wireless node. I would like some help on what I can power the UNO with.
Comment: Vin is the same as the barrel jack (they are directly connected on the PCB). The NRF24L01 requires at least 2.7v. The uno board is however very inefficient (e.g. the usb-to-serial chip is always powered).
Comment: Oh I thought that the Vin bypasses the voltage regulator but it turns out that its the 5v and 3.3v that does bypasses it, not the Vin. Despite the fact that the uno is inefficient, thats the board that I need to use. So back to the question, since it requires at least 2.7v, 4 AA batteries of  6V should be enough right? I am unable to try it out as of now as I do not have the time to buy the necessary things to try...
Comment: That is kind of pushing the limits. 6v is the absolute minimum the voltage 5v regulator requires. If the batteries are drained a bit, they will go under this 6v limit. You could use 4 rechargable (1.2v) batteries to give you 4.8V, which you can connect directly the the 5v rail. But don't expect to get more than a day of battery life.
Comment: Hmmm... Alright. Thanks for the advice. I guess if no one else has solutions I will use 6 AA batts of 9V instead of a straight 9v batt since I need a high current. Thanks!
Answer: I've used the usb battery chargers (marketed to recharge cell phones) with great success on many different Arduino boards. They come in a variety of mAH capacities and are easily recharged with any powered USB port/power adapter.
Here's a link to one I've used. (I'm not affiliated with Duracell in any way).
http://ww2.duracell.com/en-US/product/instant-usb-charger.jspx
Comment: this is certainly a easy off the shelf solution, which likely suits this user
Comment: Sorry for the long wait in accepting your answer. I was setting up the exhibition in a location that was devoid of Wifi. I eventually went for the 6AA batts. But seeing your solution, I think it is the best and easiest solution. And its off the shelf as well!
Comment: Brilliant, much easier than trying to get batteries into the DC barrel adapter, which is what I was trying to do (and can't find the barrel size/type anywhere!)
Comment: To get an idea of run time, I used this battery to power an Uno with a photocell attached for at least 16 hours. I was running a sketch to record the amount of sunlight to determine the best place for some tomato plants. The sketch didn't use any low power techniques. https://github.com/linhartr22/LightMeterLogger
Answer: Firstly if you only need short runs, go with the usb battery pack answer, but if you need the longest time from least batteries:
As has been pointed out, for best battery consumption an arduino board is not efficient due to power regulators and led lights. For best performance you want a standalone 328 chip with its BOD (brown out detector) reduced to 1.8v and then you can run it and the nrf24 chip off 2x AA batteries.
But all this might be a bit beyond you.
One thing though that will help your battery life is a PNP transistor or Mosfet on the +ve of your nrf24l01+ module triggered by a arduino io pin. as these power amplified versions dont sleep (per say, the chip does but not the PA) so it will always be consuming a large amount of power regardless of state. So just use your io pin to power it on and off for each use.
(that is unless you need it on always for recieving, in which case this wont help)


User DisplayName on first-time login

Question: Folks, we've got the problem. We are using Claims auth on a SharePoint farm.
As usual (windows auth) when user login at first-time to SharePoint site, he sees his DisplayName in welcomecontrol.ascx (rigth-bottom part of page). In this case DisplayName resolved from ActiveDirectory (i'm not sure, but it's looks like that).
But we want the same behaviour with Claims auth. All of our users sees LoginName before the UserInfoList data on SPWeb will synchronize with profile.
Our users don't want to waiting to sync-job will fill all of the user data on site (all of our users already have user profiles).

It's impossible by policies to use IHttpModule to do that on-demand
It's impossible to handle User creation on web site (EventHandlers don't work with UserInfoList)
It's impossible to use audit (because it's also need a time to handle)

What may you suggest in this scenario to sync user data on the spweb from profile on the first-time login?
Comment: Not sure what you are saying here. Is the problem that user profile synchronization takes too long and you want profile data in the meantime?
Answer: Try this Having fun with the SharePoint Welcome.ascx control

User DisplayName on first-time login


What is the point of a baking rack?

Question: I notice when I bake cookies (usually chocolate chip or peanut butter) the recipe often says "place on baking rack to cool". Because I don't have one, I just place them on a plate after removing them from the pan. It doesn't seem to do any harm. What is the point of buying this special piece of equipment?
Answer: A cooling rack serves two primary purposes.
First, it allows the cookies (or other baked good) to cool faster by letting air circulate completely around the cookie.
Second, it prevents the steam escaping from the cookies from soaking the bottoms, and other cookies placed on top.
Comment: Baking racks are also helpful for cooling things still in the pan (a cake, for instance) before removing. Or before refrigerating, if you're cooking a casserole ahead, for instance. Plates don't work for that.
Comment: I like crispy cookies. This is good to know!
Answer: In addition to hobodave's cookie-specific answer, as a general point (since this was asked as a general question) it's also quite important to have a rack if you are baking anything with a significant quantity of fat (i.e. meat).  The rack allows the fat to actually drain; otherwise the food would end up being drowned in its own fat and become soggy.  In extreme cases the fat may actually burn and seriously taint the flavour of the food you're baking.
Comment: You call cooking meat baking? I call that roasting.
Comment: @hobodave: That depends entirely on how it's prepared.  If you want to call the techniques in the chicken wing question "roasting", all the power to ya; I think most people would call them baked.
Comment: There is actually no real difference between 'baking' and 'roasting', it's just that we apply one term to savoury foods and one to sweet (generally). One could argue that the difference is the addition of fats on the outside to promote Maillard reactions, bit really it's the same thing.
Comment: For roasting meats, I rarely use a wire rack -- I just place down some carrots or other vegetables.  The only time I use a wire rack in the oven for meats is for bacon.  99% of the use my wire racks get is from baking.
Comment: @roux: Now that I think about it, I'm pretty sure you're right - just about everything, from preparation to heat levels to which oven rack you use, is exactly the same.  The only discriminator I use is the vessel - if it's a baking sheet or dish, it's baking, if it's a roasting pan or dutch oven, it's roasting.
Comment: I'm not sure I'd call anything involving meat baking, but this is also a good point.
Answer: When you place something on a cooling rack you expose more of the surface area to the air allowing your cookies, bread, etc to cool faster than just leaving them out on the pan.

What is the point of a baking rack?


How do you validate a bitcoin address using bitcoinjs library in javascript?

Question: How would one validate a bitcoin address using the bitcoinjs library? Or is there another way to do this via javascript?
Comment: Do you mean for a website or app? Or do you just want to personally verify one?
Comment: for a website im working on. I have bitcoinjs library loaded, but not sure what function to call to check if a btc address is valid or not.
Answer: If you call
bitcoin.address.toOutputScript(address, bitcoin.networks.bitcoin)

It will throw an error if the address cannot be parsed as P2SH or P2PKH, or if the checksum is not valid. Replace the second argument with bitcoin.networks.testnet for testnet.


How do I answer questions on this site?

Question: I found a solution to a question on this site that no one had provided my answer for and I wanted to share it with the world.  I cannot figure out how to answer a question.  Commenting takes "Reputation".  How do I do this?  I love this site idea but I am very frustrated right now.
Comment: As you see - 18 hours only have passed since this question & already you have over 50 rep points. The entry bar is there to stop fly-bys & spammers, not people who wish to actively participate. It doesn't take long to get that first 50 - now not only can you answer, you can comment on other people's posts too. Welcome to Ask Different ! :)
Answer: The question you've mentioned (The headphone jack on my MacBook Pro just stopped working. How do I fix it?) got protected automatically by the system because it attracted a lot of off-topic answers in the past (which got deleted so you can't see them). I've removed the protection and am looking forward to see your answer.

To get some details about protected questions, see https://apple.stackexchange.com/help/privileges/protect-questions.
To learn about reputation (points), see https://apple.stackexchange.com/help/whats-reputation
To learn more about how this (and all other StackExchange) sites work, see https://apple.stackexchange.com/help
Answer: You can answer the vast majority of site questions without earning 10 reputation on a specific site. An association bonus of 100 doesn't count in the few questions that are "protected".
Anyone with 10 rep (association or earned otherwise can comment on anyone's questions or answers.
See the help and especially the section on how to answer for more guidance.
Comment: @AaronTrimble extenuating circumstances -- the vast majority of our questions here don't have such a high bar on them for answering. The one you picked just happens to be a magnet for bad and off topic answers so it was protected.
Comment: Then I was going to just post the question and answer it myself, but I found out that you can only post every 20min... Thanks for your help.  I don't if you work for this site, but if you do, you should know this is a very unwelcome way for people to contribute.  I don't how the site can function when there are road blocks the whole way to building it up
Comment: Very few people 'work for this site'. The entire idea of SE is that it is edited & moderated by the users themselves, gaining powers with reputation, plus we have dedicated moderators, who have higher edit/delete powers.

How do I answer questions on this site?


How to configure GlassFish v3.1 to use SSL?

Question: We are looking for simple step-by-step manuals how to configure GlassFish v3.1 to use SSL. We are running few legacy application under GlassFish and we hope there is no need to change them: so that all SSL is just handled by GlassFish.
Answer: I found the following on the web:
http://javadude.wordpress.com/2010/04/06/getting-started-with-glassfish-v3-and-ssl/
I believe there is no need to modify your legacy application at all: GlassFish will pass unencrypted message to your app.


need wiring diagram for a bedroom

Question: Wiring Diagram for bedroom needed.  I will have one ceiling fan with light controlled by a three way switch then from the ceiling fan unit need power for two independent switches to control led light strips in two seperate closets. attached below is what I am thinking but I need advice / second opinion on the best and code compliant method to wire this room. I have access from attic to drop down wires where need be. I  need closet lights to be able to come on or off regardless of whether or not the ceiling fan light is on or off. Need help as soon as possible with any ideas.  All lighting will be LED and eventually be using a smart home system.  thanks for your cooperation and assistance in advance.
Comment: FWIW you should have posted your image rotated 180 degrees from what you have to make it easier to read.  I didn't notice door #2 until just now - so in my diagram, the "inside" 3-way switches are the ones at door #2.
Answer: You only have always-on power at the first switch (the 3-way by the door).  At the fan/light, you only have switched power, controlled by the two 3-way switches.  So, you need to run a 14/2 connected to the power coming from the panel (at the switch by the door) to the two closet switches to supply them with power.
You need two wires to have an electrical circuit - "hot" (black in house wiring) and "neutral" or "return" (white in house wiring).  When you wire a 3-way switch, you need an additional wire connecting the two switches:  The neutral wire is always connected, and the switches choose which of the two other wires to make the hot leg of the circuit.  When both switches are connected to the same wire, the load gets power (the light/fan comes on), when they are connected to different wires, the load is switched off because there isn't a complete circuit.
You could have an "always on" circuit at the light/fan, but you would need to run 14/4 - four conductors - between the two 3-way switches - neutral, plus the always-on hot lead, plus the two switched wires.  Then, from the second 3-way switch (the one connected to the light/fan), you would run 14/3 to the fixture, with neutral (white), hot (black) and switched (red).  At the fixture, you would connect neutral and switched to the light/fan to supply it with switched power, and you'd have the neutral and hot leads to continue to other uses, such as your closet lights.
That's not the way I would do it, though:  As I said, run a 14/2 to supply your closet lights, tapping off the mains at the 3-way by the door.  That avoids having to use 14/4 altogether, and you only need 14/2 going from the second 3-way to the fixture - neutral and a (switched) hot lead.
Referring to your diagram, instead of having a 14/2 going from the ceiling fixture to closet #2, have a 14/2 going from closet #1 to the switch by the door.  There, as I said, connect the new 14/2 to the wires coming from the panel for power.  No other changes are required from your plan.

Actually, you don't need two 14/3s, you only need one 14/3, plus a 14/2, going between the two 3-way switches because you don't need two neutral wires:

In this diagram, the blue lines represent the neutral (white) wires - which wouldn't show up well if they were white lines :)  The selection of whether to use red or black to connect the light and fan hot leads between the inside 3-way switches and the fixture is arbitrary - pick one that works.  As you can see, the white wire in the 14/3 between the 3-way switches is the neutral.  Assignment of the other four wires is also somewhat arbitrary, just be sure you have the switches connected in matched pairs.
Answer: Nope, you can't continue off the fan because you won't have always-hot and neutral there.  Keep in mind circuits are a tree topology, not a vine.   Branch off switch 1, then do one of two things:

Bring always-hot and neutral to switch 2 then to switch 4 on 14/2 cable.  Branch switched-hot and neutral from each switch to each lamp in 14/2.
Bring always-hot and neutral to lamp 2 then lamp 4 with 14/2.  From each lamp, bring always-hot, switched-hot and neutral to each corresponding switch using 14/3.
One of one, and one of the other.

Whichever is easier / most economical of cable / allows for continued extension of the circuit.
Comment: Thank you for your reply but I am not very clear on your answer due to the mention of switch 4 and lamp 2 etc.  is there anyway you could draw me a quick sketch of what your thinking or markup what I have provided.  If I am reading what you said correctly I beleive you mean to do my three way switch setup for the ceiling fan and light as I show in my diagram but for the 2 separate closets that would have their own switched led light strip I would have to run a 14/2 wire from switch at door # 1 to the first closet switch then from closet switch # 1 run 14/3 to closet #2 switch, is that correct?

need wiring diagram for a bedroom


Can different Apple ID co-exist for iTunes and iCloud backup?

Question: If I register and actually sign with an unique Apple ID  on iTunes and main account, on iPhone, in order to use different accounts between iTunes and main Apple identity (without having iTunes available on my PC), how should I change the account without losing backed-up data?
Answer: The description is not very clear, but yes, you can have different Apple IDs for iCloud and for iTunes purchases (if that's what you are asking).
To do this: on the iPhone, go to Settings > iCloud > E*nter the Apple ID you want to use for iCloud Backup* > Turn On "iCloud Backup".
Now, to setup a different Apple ID for iTunes purchases, go to Settings > "App Store" or "iTunes & App Stores" > Enter the other Apple ID to be used for purchases.
That way, you can sport 2 separate Apple IDs: one for iCloud backup and one for iTunes purchases.


Update Remote Site URL in Managed Package

Question: So I am trying to update the url of a remote site specified in my managed package.  Salesforce allows me to edit the url of the remote site and everything packages fine in my packaging org.  I am making this change within a patch package.  However when I push the patch to one of the orgs with my package installed it doesn't update.  The remote site url remains unchanged in the client's org.  It is still set to the old value.  Any idea how to update it?  Maybe post install script if possible?  Do I just need to add a redirect on my endpoint so that existing orgs will be redirected to the new remote site automatically.  Not sure what the best thing to do is.  Anyone else ran into this issue?
Answer: Remote site settings are not upgradeable in a managed package. Here is a link to the matrix describing this:
http://www.salesforce.com/us/developer/docs/packagingGuide/Content/packaging_packageable_components.htm
Since post install scripts cannot do callouts it would be difficult to update the endpoint as the Metadata API is the best way to do it. IIRC there was an apex hack to do it but not advisable and may cause security review issues.
With that said, I would put a redirect in place and then provide a warning to your users to update the setting by a specified time.
Comment: Why not just add a new remote site setting to your package?
Comment: Thanks for the link, I should have checked there myself.  Bad news on the redirect.  This is going to a force.com site rest service and is passing query parameters.  The force.com site redirect rules have to match the source url exactly and the query parameters are different for each call to the service.  I have over a thousand orgs that need the updated remote site.  Telling them to manually do it is not going to be a very successful endeavor...  Seems like there has to be a better way to do this...
Comment: That is what I am going to have to do.  That requires a full package version.  I was hoping I could update within a patch package version.
Answer: Looks like the only way to do this is by adding a new remote site and doing a full package version.  The nice thing is that we can push these packages out now so it can be seamless for the end client.


Tangent Line to $\sin x+\cos x$

Question: When is the tangent line to
$y = \sin x + \cos x$
horizontal?
I have no idea how to solve this problem. Would I use the equation of a tangent line here? Because if so i have no idea how to apply that.
Comment: where is the derivative 0?
Answer: Hint 1. A line is horizontal when its slope is $0$.
Hint 2. The slope of the tangent line to $y=f(x)$ at $a$ is $f'(a)$.
Answer: A line $y=mx + b$ is horizontal when the slope $m$ is $0$. Also, remember that the tangent line of a (differentiable) function $f$ at $x=x_0$ has slope $f'(x_0)$. So we are looking for the solutions of $(\cos x + \sin x)' =0$.
Since $(\cos x + \sin x)' = -\sin x + \cos x$, we want to find $x$ such that $- \sin x + \cos x = 0$, i.e., $\cos x = \sin x$. We can then proceed by noting that whenever $\cos x = 0$, we'll have $\sin x = \pm \sqrt{1- \cos^2 x} = \pm 1 \neq 0 = \cos x$, and then $x$ won't be a solution. That allows us to divide by $\cos x \neq 0$, and we obtain $\tan x = 1$, with solutions $x = \frac{\pi}{4} + k\pi$, with $k \in \mathbb{Z}$. For those values of $x$ we'll have $f'(x) = 0$, the tangent line will then have null slope, and thus will be horizontal. Can you calculate the tangent lines at those points?
Comment: Looks great now.
Answer: Hint: $\sin(x)+\cos(x)=\sqrt{2}\sin(x+\pi/4)$
Answer: Recall from calculus that a tangent line's slope is found by $y'=\frac{dy}{dx}$, therefore, we need to find when $\frac{d}{dx}\left(\sin{x}+\cos{x}\right)=0$. Finding the derivative of $\sin{x}+\cos{x}$:
$$\frac{d}{dx}\left(\sin{x}+\cos{x}\right)=\cos{x}-\sin{x}$$
Setting this equal to zero:
$$\cos{x}-\sin{x}=0\implies \cos{x}=\sin{x} \\ \therefore \frac{\sin{x}}{\cos{x}}=\tan{x}=1 \implies x=\tan^{-1}{1}$$
We can now extract the solutions as: $x=\frac{\pi}{4}+n\pi, \forall n\in\mathbb{Z}$. This gives you the solutions for the $x$-positions where your tangent line is horizontal.
Hope this clears things up!
Answer: Below is the plot of $f(x) = \sin(x) + \cos(x)$ drawn in blue. The tangent lines are drawn in red and pink.

As you can see from the plot, the tangent lines to $f(x)$ is horizontal at the maximum and minimum points. Also, it is again a sinusoidal function with a phase shift and an amplitude greater that $1$. This can be seen from the manipulation below.$$f(x) = \sin(x) + \cos(x) = \sqrt{2} \left( \dfrac1{\sqrt2} \sin(x) + \dfrac1{\sqrt2} \cos(x)\right) = \sqrt{2} \sin(x + \pi/4)$$
Now it should be clear where the maximum and minimum should occur. The maximum value of $\sin(\theta)$ occurs at $\theta = 2n \pi + \dfrac{\pi}{2}$ and the minimum value of $\sin(\theta)$ occurs at $\theta = 2n \pi - \dfrac{\pi}{2}$ and it is at these points the tangent line will be horizontal. Hence, the tangent line to $f(x)$ is horizontal at $$x + \dfrac{\pi}4 = 2n \pi \pm \dfrac{\pi}2$$

Tangent Line to $\sin x+\cos x$


Completely new to apple tree care in Alabama, any tips?

Question: Completely new to the site, and have never had more than a small garden in my yard, but I'm about to move to a decent plot of land (~40 acres) in northern Alabama. Near the house are a couple of apple trees my great-grandfather planted that are looking like they are in pretty rough shape. I'm hoping to do what I can on the place, including hopefully getting the apple trees to pull through. Does anyone know of any resources available for learning about caring for fruit trees (or for that matter, bees, bats and any permaculture tips)?
Answer: First, go here: Alabama Extension. This site contains information specific to your state. Review the tree pruning and orchard links for help with your great-grandfather's trees, but you should be aware that they may be at or near the end of their normal lifespans. You should also check for information on grafting - it's possible that you could graft twigs from your family's trees onto a different root stock and propagate them for the next generation.
Next, you might want to go here: Alabama Master Gardeners. You could become a Master Gardener - or at least take the coursework. This should provide you with some of the basic information you're looking for.
Comment: Thanks for the links. I figured there was a good chance of not saving them, but at least they're still alive. Hopefully I can get some remnant to pull through.
Comment: I forgot to add that you can try grafting smallish branches onto a very young apple tree purchased from a nursery. You might even be able to effectively replace the tree's own branches with grafts from your trees. If you feel intimidated by the process, you could contact a certified arborist who may be able to perform the grafts for you.
Answer: Watch for deer activity. If you have deer you will need a fence that is 9ft tall above ground, and extends 1 foot below ground to keep out burrowing animals like rabbits, woodchucks, etc.
Deer can easily jump a 5-6ft fence, get a 9ft fence. Even with a 6ft fence my friend would find deer trapped in his little fenced in orchard as the deer did not have enough room to get a running start to jump back out.


What's the best way to fix this horrible drywall patch job?

Question: Is there a technique I should use to smooth this in so it doesn't look this bad? Before paint I thought it looked fine but it's obvious my drywall skills are not as good as my other ones.
Comment: see https://diy.stackexchange.com/questions/63753/fix-bad-drywall-mudding-paint?rq=1
Comment: It's a tough spot, you'll need to mud a much larger area, all the way to the trim and under the wall switch plate and further up and down.  Sand it flat, apply the patch in a few light coats.  I have mad respect for drywall pros, they make it look easy.
Answer: It's very difficult for a beginner to mud in the vicinity of recepticals and switches. My advice is to cut well around the switches and then tape and mud the three joints. It would require removal of the door moulding but when your done you'll find it was very easy.

This gives you all the room you need to apply your mud with a full size blade, making it much easier to blend the mound in.
There is no such thing as a flat wall every joint in the house is raised a little bit. The trick is to make it so gradual that it is imperceptible.
Make sure you cut an approximately 45° bevel in all your butt joints with a sharp knife. Set your tape in the vertical joint. Let it dry. Set your tape on your horizontal joint without overlapping. Let it dry. Sand. 1st coat vertical, dry. Sand 1st coat horizontals, let dry sand. Repeat 3 coats after you set the tape.
You should try to finish each coat as if you don't have sandpaper.
Answer: I would re-patch it.  I've typically done small fixes around the house using a small piece of scrap (like a 1x4 behind the opening, fit new piece in, screw new piece to 1x4 [which is screwed to drywall higher up the whole] and apply a light coat, sand, repeat until desired).
I recently watched this video, which was a totally new technique to me.  Might be worth exploring, if you're more comfortable with this approach.
Comment: Re the video: I could be wrong but it seems to me that it a sharp knock on that spot could crack that patch job.  Interesting idea but I'd add some support behind it.
Comment: Yeah, I've never tried it before - but I would add a piece of scrap wood behind it if I ever tried this.


Getting data of area covered by polygon in ArcGIS Desktop?

Question: We have a layer that contains land parcel information such as area for each parcel, and a unique parcel ID. We also have multiple polygons that cover some parcels. We're trying to figure out how to determine which parcels are covered by the polygon and which parcels are not covered by the polygon.
Answer: You could try a Select by Location, and for the target layer use the parcels, and for the source layer use the polygon layer, and for the selection method use either- are within or are completely within the source layer feature.
Then you can use the switch selection in the attribute table to see which ones are not within the source layer.
Answer: Look at the analysis toolbox in the geoprocessing tools. There are many ways of doing what you want. A basic union is probably the easiest as any attributes from the polygon will be added to parcels it overlays.


What knife and cutting technique should I use for cubing bacon?

Question: I like to fry and cook cubed bacon for various dishes, but I sometimes have a hard time cutting through bacon, especially where the fat meets the meat. The bacon just tends to move around too much, and it gets trickier at the end of the slice (or chunk). I usually use a 6 inch serrated knife for this task. What knife would be best - serrated, chef's, or filet? Or something else? Is there some special technique I should be using?
Answer: Cutting bacon into cubes was a regular prep task for me when I was cooking professionally, so I got very fast at it.  Here are the tricks I found:

Fully cooked (baked) bacon cuts MUCH faster and cleaner, and you can make perfect cubes
Don't use a serrated knife.  It'll be easier to cut with, but it will shred and fray the bacon as you slice, eventually making a mess.
Use the sharpest knife you have, especially for uncooked bacon.  There's already a tendency for it to slip and slide around, and a sharp knife cuts with less back-and-forth motion.
You want a deep-bellied knife such as a santoku or Chinese cleaver, because you can slice through multiple stacks of bacon at once.
Stack slices of bacon so you can cut multiple pieces at once.
Try to work with 4" by 4" blocks of bacon, so the pieces aren't big enough to slip around as much.  With this size you're still able to do a lot at once, but it's fast
Organize your cutting board.  Pick one corner for whole chunks of bacon, then cut into strips and move to another spot, then finally into cubes which goes in another spot.

Now if I were a culinary school, you'd have paid a few hundred bucks to learn what I just told you.
Comment: Back when I used to work at a restaurant, the kitchen would use pork belly, not bacon (which is cured and smoked).  The prep was to braise a large block of pork belly, something like 8" x 8" x 2" (thickness) slowly for a few hours.  They'd let it cool and refrigerate it.  The next day, they'd cut the chilled block with a non-serrated knife as you've suggested.  This would result in true "cubes".  It's possible to make a pork belly into bacon using this same process, so long as one has the patience to smoke and brine it first.
Comment: @EricHu Yes, when I say bacon, I mean house-cured bacon.  We also started from big slabs of pork belly, cured it in the walk-in, and smoked it. We actually used an improvised smoker made from 2 deep full hotel pans plus a slotted insert, with hardwood below.  The whole thing sat on a heat source to char the wood and smoke the bacon.
Comment: @EricHu That setup is probably inadvisable without good ventilation.  I'd do it outdoors or somewhere with a proper vent hood (what we did).
Comment: Cool tip, another culinary school lesson :)  Is it feasible to use that setup with an oven without resulting in a smokey kitchen?
Answer: I first remember seeing Melissa d'Arabian demonstrate using KITCHEN SHEARS to cube bacon during her season on "The Next Food Network Star". I tried it soon after and I find that the scissor action of the shears makes it EASY to cube bacon. Clean, consistent easy to use.
Answer: I would say a chef's knife, for sure. Make sure it's sharp! If you've never sharpened your knives (not just honed using a steel) it can make a world of difference.
If you are having troubles, making sure the meat is chilled will help. Straight out of the fridge works okay, but it is even easier if you throw it in the freezer for 15 minutes or so.
Answer: Just use a slicing machine for the first 2 cuts (1st=slices, 2nd=stripes) and a sharp blade for the 3rd cut (the cubes). That's probably the fastest and most precise way to cut lots of them :)
Guess I should mention one trick: put them in the fridge/freezer for a while ...
simply because fat on low temperature is way more easy to handle.
Comment: I'm not Kramer, I don't have a deli slicing machine at home. Sorry!
Comment: There are no bones in bacon.
Comment: You could ask at the butcher's to get them boned out & sliced there already.
Comment: What we have here (as seen on the picture above) ... there's ordinary 2 soft rips contained, which should be removed prior to cutting... even if they're not exactly a bone :)
Answer: Stack and slice with a large santoku or cleaver (you'll need the weight, depth and relatively flat blade)
Answer: I use a pair of scissors. This is clearly the most underrated kitchen utensil. I've written an article about my top five - scroll to the bottom to see the scissors.
One huge advantage is that you can do it straight onto the frying pan leaving only the scissors and your fingers for cleaning :-)
Comment: Welcome to Seasoned Advice! We're a Q&A site, so we ask that you only link to things if they're actually part of your answer. In this case I don't think the link provides any additional information for this question, so it's basically just an unsolicited advertisement for your site, which is definitely not allowed here. Since this is your first post I'll just edit it out for you, but please refrain from doing this in the future.


Printing Comments with PDF

Question: Is there a way to print the comments that are associated with a pdf on the linux version of Adobe Acrobat 9? Both acroread and evince display the comments just fine, however the linux version of the reader lacks the button in the print dialogue to enable printing comments.
Specifically I'm looking to recreate this feature (image taken from adobe.com) where the comments are printed on a seperate page with lines to the main document indicating where the comment was inserted.

Please Note: I am not asking to modify or write comments and annotations (typically a feature associated with Acrobat Pro), but to merely print them in a conveniently readable way.
Answer: You need to click Summarize Comments button at the bottom of File > Print screen.
Comment: This button doesn't exist in the version of adobe acrobat that is in the ubuntu repo's

Printing Comments with PDF


Merge tags [jigsaw] and [java-module]

Question: Both of these refer to the Java Platform Module System -- technically the JPMS is a "component" of Project Jigsaw, but in practice the JPMS was Jigsaw's main deliverable, and questions tagged jigsaw are overwhelmingly about the module system, not about other aspects of Jigsaw such as the application of the module system to the Java platform. There's no obvious systematic difference between questions tagged one or the other, and in fact many questions are already tagged with both.
Answer: Tl;DR Both tags have the right to exist.
jigsaw155 Open Qs 32 watchers

Project Jigsaw aims to design and implement a standard module system for the Java SE platform. It was released as part of Java 9.

java-module 174 Open Qs 8 watchers

Refers to the module as defined by the module system in java introduced in Java9. Hence likely to be coupled with Java9 (or above) tag.

Both: 31 Open Qs
5 names of the 8 most prolific answerers in each of the All Time Top Answerers' lists are the same.
A merge would not be appropriate because, even if in practice the two tags are used to mean much the same thing their Usage guides and wikis are different:
jigsaw wiki:

Project Jigsaw is a sub-project of OpenJDK that aims to provide a standard module system for the Java SE platform. Originally targetted at Java 7 it was postponed first to Java 8 and more recently to Java 9.
Originally the scope of the project was to provide modularisation for the JDK itself. This scope has been expanded to make the module system part of the Java Platform.
The Jigsaw project is closely related to the Penrose Project that is looking at interoperability between Jigsaw and OSGi.
w project is closely related to the Penrose Project that is looking at interoperability between Jigsaw and OSGi.

java-module wiki:

A module is a named, self-describing collection of code and data. Its code is organized as a set of packages containing types, i.e., Java classes and interfaces; its data includes resources and other kinds of static information. The only module known specifically to the module system, in any case, is the base module, which is named java.base
A module is described using a module-info which itself is a new construct added in java-9 to provide a module definition.
Module names, like package names, must not conflict. The recommended way to name a module is to use the reverse-domain-name pattern that has long been recommended for naming packages. The name of a module will, therefore, often be a prefix of the names of its exported packages, but this relationship is not mandatory.
Module declarations are part of the Java programming language, rather than a language or notation of their own, for several reasons. One of the most important is that module information must be available at both compile time and run time in order to achieve fidelity across phases, i.e., to ensure that the module system works in the same way at both compile time and run time. This, in turn, allows many kinds of errors to be prevented or, at least, reported earlier—at compile time—when they are easier to diagnose and repair.
The Java SE 9 Platform Specification will use the module system to divide the platform into a set of modules. An implementation of the Java SE 9 Platform might contain all of the platform modules or, possibly, just some of them.
A java.lang.Module represents a run-time module, either named or unnamed.
Named modules have a name and are constructed by the Java Virtual Machine when a graph of modules is defined to the Java virtual machine to create a module layer.
An unnamed module does not have a name. There is an unnamed module for each ClassLoader, obtained by invoking its getUnnamedModule method. All types that are not in a named module are members of their defining class loader's unnamed module.
The package names that are parameters or returned by methods defined in this class are the fully-qualified names of the packages as defined in section 6.5.3 of The Java™ Language Specification, for example, "java.lang".

In the Glossary Merge only covers duplicate Qs and I have failed to find clear guidance anywhere on the difference between merging for tags and synonymising but seem to recall that the latter is reversible, in extremis, and the former is not, so synonyms are generally preferred.
There are just enough users qualified to propose and carry a synonym, in either direction. A merge should not be imposed upon subject matter experts  when it seems they do not want even a synonymisation, and lack of such has little significance for other users.
However a clean up may, as usual, be appropriate.

Merge tags [jigsaw] and [java-module]


Excel 2007 conditional formatting rule using formula to highlight a row based on matching text between columns

Question: I am checking accountability of whether my office is creating source acknowledgement reports "C", recommended whenever a reference document "A" is read, and required whenever an article "B" is published that cites information from reference document "A". Both reports "C" and articles "B" cite the serial numbers of reference documents "A", and I can export spreadsheets from two different systems to create lists which count each separate type of document published for a specified period of time: one worksheet lists identifying data (including the source doc serial) of source acknowledgement reports "C"; the other list identifying data (including source doc serial) of articles "B".
By putting the data on separate worksheets in the same spreadsheet, I can identify which source acknowledgement reports were written about reference documents whicher were cited in articles by using this formula in worksheet 2:
<code>=IF(ISERROR(VLOOKUP(A1'SHEET1'!$A$2$A$160,1,FALSES)),"",VLOOKUP(A1,'SHEET1'!$A$2:$A$160,1,FALSE))
</code>
It seems I have to insert the column of serial numbers matching both lists from worksheet 2 into a new column (B) on the article worksheet 1 in order to  use the conditional formatting function in Excel 2007 (it won't work with multiple worksheets).
My problem is I want the conditional formatting rule to highlight each entire row green in the article worksheet 1 (but I will settle for just the serial # cell) if the serial # in one of worksheet 1's Column A cells matches any of the serial numbers inserted in worksheet 1 column B.
Answer: Is this the sort of result you are aiming for?:

(with Applies to =$A$2:$E$9).
Comment: YES! That was it, pnuts! I was forgetting to make the "Applies to" cover the upper-right to lower-left ends of the data.  Thank you!


What are the rules for a space marine commander?

Question: I was searching the space marines section at a local warhammer shop when I saw a miniature called the space marine commander, I looked for it in my index but his rules weren't in it. What are the rules for a space marine commander? Do they follow the same rules as the captain? Please let me know so I can decide whether to get him or not.
Answer: Was this Space Marine Commander the miniature you saw?
If so, at least according to the description on the website, it appears you'd be treating this as a Captain for rules purposes:

Space Marine Commander
A Captain leads each of the ten Companies of a Space Marine Chapter. They are second in experience only to the Chapter Master and each is a warrior so deadly that he will rarely meet his match. Each Captain is an inspirational and determined leader, able to coordinate the Space Marines under his command whatever the opposition.


Singular-Plural agreement

Question: I am a little bit confused about the use of "each" with the correct noun.  For example, for the use of "each" Which expression is correct?
Each of the previous month or each of the previous months?
Answer: ...each of the previous months is correct, because you are selecting from multiple months. Compare to ...each of the previous five months, or ...each of the previous twelve months.
Unless, of course,  this fragment is meant to be possessive. That's another issue altogether.
Comment: My only argument is that I have learned in old grammar school that 'each' always is treated as 'singular' and so the noun following it should be singular as well.
Answer: Months is correct as Davo mentions.  It might be helpful to think of it this way:

Each month during the last twelve months...

Your phrase is conveying the same idea in a less specific sense.

Singular-Plural agreement


What kind of cypher do Ubuntu uses on its full disk encryption?

Question: One important thing that make me install 13.04 instead of the stable 12.04 LTS is the encryption of the installation. I want to achieve the same in Windows 7 with TrueCrypt.
I want to know what kind of encryption do Ubuntu uses for the disk encryption utility that comes with 13.04+ (AES, Serpent, etc... / Hash) and so I would like to know if only the installation filesystem is protected or the swap is also cyphered (whole disk).
Thanks!
Answer: Ubuntu uses AES-CDC by default.


How to express myself in a sensible way

Question: I find really hard to express myself I mean it's pretty difficult write clearly what I mean. Any time I try to write something even for my job I am stuck, I look at the page and no words come to my mind and I feel lost I really don't know how to tell what I need to say.
To be honest now this problem is becoming a real obstacle because I have to write email to customer of suppliers. My manager constantly corrects my email saying that they don't make sense and some times are too rude.
Answer: You can try to "rubber duck".
Explain what you need to convey out loud to someone not in the know or even to a rubber ducky from the bathtub. Then write it down.
When still unsure, wait a day and read it back to see if the text still makes sense.
Keep at it, talk about it, it is a learn-able skill!
Answer: There is a three part solution to your problem:

Format -- there are some standard forms for business
communication.  A lot of what makes any communication seem more
polite is just the inclusion of some standard niceties (please,
thank you, etc) that can basically be cut and pasted from one email
to the next.  You should easily be able to find some books or online
tutorials for business communication.  If you follow the pattern, all you need to do is adapt it to your situation --it doesn't need to be creative or inspired.
Rewrite -- never send an email until you have read it through a couple of times.  It may help to read it out loud.  It might also help you get started on your writing if you tell yourself that the first version doesn't need to be perfect, since you'll be rewriting later.
Practice -- no one is good at writing until they do a lot of it.
Answer: I feel a very good and simple way to start is a scratch pad. Hard to express is generally associated with difficulty in forming sentences which convey the intended thought. We always have the basic words ready, but the sentences is what the problem is.
Just write whatever comes in your mind. Words or sentences or pictures whatever it may be. First put all of it down somewhere.
Let these just be random dots for now. The next task is to join the dots. Just repeat this iteratively and form sentences. Finally you will get the intended. Initially you may have to do this if you are really having a hard time expressing but once you get a hang of the procedure. You will do away will at the putting down part.

How to express myself in a sensible way


Need help- Documentation for non-technical people using Agile

Question: Now we are using Agile and hardly create BRD\FRD, we create user stories, and all this is good for everyone working in the same department. Including the stakeholders. However, if I would like to share the requirements with a person in any other department, who has not heard of Agile. How can convey what the product will do? I can give a demo; however, I can tell the rules and however, they might not remember all, and won't be able to refer to something substantial. If I write on a document and read it to them with details. Here, I don't like the idea of reading from a document because it gets boring. Also, I could add pictures to it and make it little interesting. However, for this I will need to go through user stories and create a document, this I don't think is the best way. So, please guide me how can I solve the problem of sharing the details of a project(Requirements, limitations, etc) to a non-technical person. Thanks!
Comment: What did you do before agile? You didn't just drop a binder with the BRD/FRD on peoples tables, did you? Why can't you do the same you did before?
Comment: Hi! Agile teams create a good amount of documentation (many of them do at least). However, it has a tendency to be more specific to its purpose. In the scenario you are facing, what is the goal you are trying to accomplish with the documentation? Also, User Stories usually make terrible documentation, which I why you find them inadequate. That's not really what they're for.
Comment: There are lots of ways to send your messages. See below...
Answer: TL;DR
There is no silver bullet. However, it is likely that your organization needs to adopt a more comprehensive set of agile tools and practices to reduce unnecessary or burdensome documentation.
Agile Practices Often Deliver Better Documentation
Your question is possibly too broad to answer, but I'm going to go out on a limb and guess that your organization has recently transitioned to "Agile" (whatever the organization thinks that means) without having actually adopted the complete framework, or without implementing common agile practices like Test-Driven Design (TDD) or Behavior-Driven Development (BDD). This is likely the source of your problem.
Agile frameworks value working products over extensive documentation. The Agile Manifesto says:

Working software over comprehensive documentation...[T]here is value in the items on the right, [but] we value the items on the left more.

This doesn't mean agile teams don't document anything. In fact, high-performing agile and DevOps teams often produce more useful documentation than they did before adopting agile practices. This is generally because:

"Living documentation," like well-commented and frequently refactored code, is often more accurate than dead-tree hieroglyphics from the misty dawn of time when the initial requirements were most likely generated.
When properly-written, TDD/BDD/ATDD tests read like natural-language documentation, and often incorporate terms and concepts from the the product's business domain and a user's point of view.
Continuous integration using good tests ensures that your documentation remains both current and accurate, which is something that most traditional projects fail miserably at.
End-user or system documentation (if and when actually needed) is often compiled programmatically from code comments, executable tests, API signatures, and so forth. Note: This requires both good practices and good tools.
Any necessary documentation that isn't self-generating should be part of the Definition of Done for each Product Backlog Item (PBI) and the iteration's Increment.

In Scrum, you should have demonstrable increments of work every iteration. This is often more valuable than dead trees, because it represents a potentially-shippable increment and something the stakeholders can see (and often touch).
Maximize the amount of work not done by eliminating unnecessary documentation, and focus on implementing the practices that reduce truly essential documentation tasks to manageable proportions.
Answer: FRD is a way to document (in a waterfall way) what the intended functional requirements are. This doesn't usually document actual implementation. Using agile methods, you can better communicate to non-technical staff what is actually being delivered. Here are some suggestions to allow for comprehensive documentation while staying agile and productive:

Have the technical writers be a part of the project team, creating
technical and non-technical product documentation iteratively. You
can add "product documentation completed" as acceptance criteria for your user
stories. The official product documentation can be your living document.
Hold a pre-launch high level demo (via your product manager). This high level demo can help marketing, sales, and department managers understand what is being delivered. You could add this to your sprint review processes.
Add more in-depth internal training considerations to your launch
delivery checklist so you can consider it for each sprint or release. You can flag epics or stories as requiring internal training and who should be responsible for performing the training.
Hold more detailed internal trainings (i.e., train the trainer) for interested
internal stakeholders (such as customer support and trainers).
Record these and have the video available for those who are
interested to reference. Add a link of the video to your project reference
documentation. The internal training can be very helpful to identify trends in questions that you may want to answer within the official product documentation.
Answer: Right off the bat I can think of 3 ways to communicate outcomes and requirements:

Invite Stakeholders to Sprint Review or maybe Daily Stand Up
Show Stakeholders your product's Information Radiators
Update the Product's wiki/Slack channel:

Have an overview of the Product's outcomes/KPI/requirements known from the start (with slides or any other documentation)
Focus overviews on delivering Value (gaining: $/user info/etc and reducing: costs) and share as needed
Have Team Members add additional detail and overviews of Features as the Product evolves and new info emerges

If Agile is new to your culture make sure that Stakeholder communication goes through the Product Owner and/or the Scrum Master. Those 2 roles will ensure the Dev Team is not derailed by outsiders.Good luck!
Comment: Be careful inviting stakeholders to the daily scrum. That's technically for (and by) developers only and anyone visiting needs to be well aware of the "shut your mouth" rule.
Comment: Whilst well meaning, this answer is a stock response and does not answer the OP's question.  How does "Focus on delivering value" help the OP?  That is a generic mantra.
Comment: @Venture2099 My guards go up when I see "generic mantras" in these forums too. The OP's call to action was: "please guide me how can I solve the problem of sharing the details of a project (requirements, limitations, etc) to a non-technical person". Engaging non-techs with documents they won't read or understand is a waste of resources. Why not just get them involved in the process through the ceremonies (with Scrum Master supervision)? PS: this is a common problem so a "generic" answer may be a good one.


What happens if the runner choses to play [Magnum Opus] twice?

Question: Is there any benefit to installing the same card twice? Particularly a card like Magnum Opus? (I understand the point for most hardware and the like, but what about ice breakers and magnum opus)
Comment: It's unclear what you mean by "playing" in this case. Do you mean having multiple Magnum Opuses installed? There is no benefit to installing more than one, as each Magnum Opus must be activated individually and all do the same thing: giving you 2 credits for spending 1 click. Putting multiple copies of MO in your deck, however, increases the likelihood that you will draw it during the game, or draw it again if one was lost due to damage
Answer: The answer provided by @user30903 in the comments is correct, and I believe your question effectively clarifies what you mean by "playing" as you also reference icebreakers. There is no benefit in installing Magnum Opus twice at the same time: the effects do not stack, and in fact it is detrimental due to the memory usage. The same is true of each individual icebreaker - they do not stack so there is no additional benefit to having two identical ones in play at once.
There is a benefit to having multiple copies in your deck, to raise the chances of drawing it at a useful time.
Similarly there may be benefits to installing it twice during the course of a game, for example if the first copy if destroyed somehow, but not at the same time.
The only (niche) case where I can think it might be useful to install M.Opus or an icebreaker when you already have it in play would be if you were over the hand limit, desperate not to discard any hand cards, and worried that your original copy was going to be destroyed. Then there might be a reason to install a copy, but it is likely to be an expensive solution.
Edit: Thanks to the comments for pointing out several counter-examples of icebreakers where you would want several copies of the same card installed. In general you wouldn't, but there are exceptions. My answer holds true for M.Opus.
Comment: "The same is true of each individual icebreaker - they do not stack so there is no additional benefit to having two identical ones in play at once." Atman is sulking in the corner.
Comment: There are a few others, too: spike, shiv, crowbar, Cerberus, Cyber-Cypher, Faerie, Caissas, Overmind, Chameleon. The point is, it's probably worth saying something like "most individual Icebreakers", since there are so many counter-examples.

The broader point is that many installed cards have paid abilities with no limitations on how many times you can pay for them, and for those cards one would only very rarely want a duplicate installed.
Comment: Hah! That is an excellent counter-example... I'm going to leave my answer as-is because I think Atman copies with different strengths are almost like different cards, but you're completely right, that is a definite reason for playing multiple copies of the same card at the same time.
Comment: Mongoose too. :)
Comment: and, upvoted. :)


Intrinsic Viscosity

Question: I'm presently undergoing an Experiment for the determination of the viscosity of Ficoll-70 using Ostwald viscometer to calculate the time and a digital weighing balance to determine the weight of a specified volume of the solution at different concentration. I have reached a result but unable to correlate with any data provided by the journals or thesis on this area. It's because they all have given the value of 'Intrinsic Viscosity'. How different is the Dynamic viscosity from the Intrinsic one? Can I calculate the dynamic viscosity of a solution if I know its Intrinsic viscosity ?
Comment: According to the Wiki-page, Intrinsic viscosity is quite different from Dynamic viscosity: http://en.wikipedia.org/wiki/Intrinsic_viscosity
Answer: Your viscometer measures the viscosity of your Ficoll-70 solution. This viscosity is made up partly from the viscosity of the water and partly from the viscosity of the Ficoll-70 dissolved within it, and obviously the viscosity you measure increases with the concentration of Ficoll-70.
Intrinsic viscosity is a rather different concept. It's really a measure of the shape of the solute at infinite dilution, or at least sufficiently dilute that you can ignore three or more body interactions. For these low dilutions it's the shape of the solute that determines the viscosity, and the intrinsic viscosity depends on this shape.
At very low concentrations the dynamic viscosity will be given by:
$$ \eta = ([\eta]\phi + 1)\eta_0 $$
where $[\eta]$ is the intrinsic viscosity, $\eta_0$ is the viscosity of the solvent (presumably water in this case) and $\phi$ is the concentration of the Ficoll-70. You'll probably find $[\eta]$ is given in units of ml/g, so you need to give $\phi$ in g/ml. You could try calculating the viscosity using this formula, but I'd be suprised if it worked for the sort of concentrations Ficoll-70 is normally used at i.e. a few percent by weight.
Later: I note that https://somapps.med.upenn.edu/pbr/portal/immune/Ficcoll_info.pdf gives the relative viscosity of Ficoll-70 as a function of concentration. You could use this to check your results.

Intrinsic Viscosity


What is the difference between Pasta Sauce and Spaghetti Sauce?

Question: I'm deciding to make spaghetti squash today but can't decide what sauce to use: a pasta sauce or spaghetti sauce. I'm sure those are just general terms for many types of sauces, but can anyone give me an idea of the difference between the two? And also, what is marinara sauce?
Comment: @GdD It's obviously not a perfect substitute, but some people do use spaghetti squash as a substitute for spaghetti.
Comment: @Axop51 Welcome! Unfortunately, "what goes with X?" is off topic here (what toppings you'd like is more about searching for recipes and suiting your preferences than a specific question), so I'm editing that out of your question. The rest is fine, though.
Comment: Why would you use pasta sauce on squash?
Answer: Marinara sauce is a specific sauce, made with tomatoes, and probably garlic, onions, and herbs.
Spaghetti sauce, in the US, means something tomato-based, possibly with meat. I suppose it's based roughly on marinara or bolognese, depending on what variety you have.
Pasta sauce means absolutely any sauce you can put on pasta. Maybe some people have specific things in mind, certain sauces they use more often, but it's not a specific enough term that you can say "I'm making pasta sauce" and have everyone know even roughly what you mean. In the US, certainly tomato-based ones are extremely common, probably followed by creamy things like alfredo, but there's plenty beyond that.
Answer: This is not cut in stone, but I have heard people saying that spaghetti sauce needs to be 'stickier' than just any pasta sauce, because it has to coat the spaghetti enough to get a good balance of pasta and sauce.
You will find additional tricks for that, like not rinsing your spaghetti after cooking, letting it dry completely before adding the sauce, or using some of the cooking liquid in the sauce, so that it has a higher starch content.
That says nothing about the taste of the ingredients, only about the consistency. You can choose your ingredients to make a thicker sauce.
I noticed that letting my onions simmer for a long time, then again letting the sauce simmer for a long time, helps.


Why didn't Arya use the powers of The Faceless Men to get past the dead in the library?

Question: In the War of Winterfell in Game of Thrones S08E03, we see Arya terrified in the library. Why didn't she change herself to appear as the dead in order to get past them?
Comment: Sure. I want to keep the question open for some more time, to read other people's perspective.
Comment: I think Paulie_D's answer sums it up as best one can, but I think there is nothing wrong with asking questions based on magical semantics, even if we don't have a lot of evidence to support a possibility of something being asked. It's not impossible assumption, just not a lot of evidence to support it would work 1+
Comment: Ya, I mean there may be something to the condition to what one's face needs to be in order to use it. So maybe Arya didn't have the time to prepair it either? Plus I think there are many characters that are "living-dead", but the semantics on them have been different...
Comment: At what point between the opening scene and the library did she have the opportunity to collect an undead face?   If she doesn't even have time to perform that first step then there's nothing else to consider.
Comment: She didn't us her powers? Seems like she pretty much disappeared without a sight when the wight heard her blood drip. Also, it doesn't seem like visual reception is the kind of dominating factor for the undead as the living.
Answer: Because appearing dead is not the same as being dead.
Firstly, we do not know the extent of the shape-shifting abilities of the Faceless Men but these appear to be based on appearing as something other than what you are.
The Dead are targeting the living and there is no indication that the abilities of the Faceless Men can make you be sensed as "unliving" to the Dead.
Essentially, if Arya is alive, she's targeted by the Dead, regardless of what she looks like.


What is the purpose of having lives?

Question: I think in game design it is incredibly important to ask the question why about everything, especially something that has become so standard as lives. So I am asking, what is the purpose of a game having the concept of lives? Why have lives?
Comment: Just because nobody has mentioned the elephant in the room yet:  Modern games don't have "lives" any more, and haven't for almost a decade.  I'd really like to see an answer which also talks about the purpose of NOT having lives.
Comment: @JalalAldeenSaa'd most cheat codes are actually leftovers from development. It is useful to have access to several features instantly, instead of accessing them in game by common way, which may take time.
Comment: @Maik Nobody called Jack here ;-)
Comment: touché @Duck :D
Comment: A good question, another question is why have a "cheat codes" also?
Comment: Judging from the answers there appears to be confusion whether this question is "Why have more than one life?" or "Why not have unlimited lives?"
Comment: @Jalal Aldeen Saa'd A lot of modern games don't have cheat codes either.
Comment: I see why cheat codes are very useful. They might not be good, but once I passed a game normally, why shouldn't I have some fun?
Comment: So you can display 30 second video ads every time the lives run out.
Comment: Even with Arcade.SE in existence this question still wins my "best question title" award.
Answer: Other than the arcade/profitability/limiting play factor, quite simply lives add tension.
If falling off a cliff doesn't mean anything (namely, there's no punishment), then you won't feel bad when you do it.  But if you fall off too many times and can't proceed, then you want to make damn sure that you don't fall off the cliff.  Harder games make you feel better when you beat them, it provides bragging rights, etc.
Of course, that kind of compulsion loop player punishment has gone by the wayside recently.  Taking up the player's time is punishment enough.  When most research shows that people don't finish games as it is, game designers are trying to find ways to make it less frustrating to go through the game but providing enough of a challenge that it's enjoyable.  Basically, it's less about the game and more about the experience.  Lives would be inappropriate in a game like Uncharted, for example.
Comment: @poke I think you're misunderstanding the point.  Without getting too philosophical, what is death without lives?  There are a lot of games with deaths that don't have the concepts of lives.  The point I was making is that without limiting how often you can die, death becomes meaningless.  If you want death to mean something (not to imply that death should always mean something), you need to have ramifications for dying. Hence, lives as a resource.
Comment: I use the word "research" in a pretty loose term.  With the advent of achievements a lot of companies have added trivial progress-based markers.  You can use that data to see what number of online-enabled players have completed an early level and compare that to the number who have completed the end of the game.  As a public example, only slightly more than half of players beat HL2:Episode 1 http://www.steampowered.com/status/ep1/?gamesHelp#HighestMapPlayed
Comment: I think this answer only explains why there is "death" within games. But under "lives", I understand a number-limitation of how often one can die without losing a lot process in the game.
Comment: +1 for mentioning some research (references would be awesome, but not needed because what you wrote makes sense), and for pointing out that lives aren't appropriate in all games.
Comment: "[L]ives add tension. If falling off a cliff doesn't mean anything (namely, there's no punishment), then you won't feel bad when you do it." So you see "invulnerability" as the opposite of having lives? I thought the opposite of *lives* would be *a* *life*. Try NetHack if you want tension. ;)
Answer: Profitability...
Extra lives provides the player with additional "chances" to "try again."  Particularly with traditional arcade games back in the 1980s, a player would insert a quarter (25 cents) to play the game, and with this payment they'd get a number of lives (usually 3 or 5).
With these extra lives, the gameplay is longer, and the player gets more "value" out of the game since they extra lives allowed them to automatically continue the gameplay.  If the game provided only one life, they player might not enjoy the game as much (because the game would be a shorter duration), and consequently may not insert as many quarters to play again later (which would make it less profitable).
When enjoying video arcades in my younger years back in the 1980s, I noticed that the games that provided more lives tended to be more popular.  I'm sure the arcade game vendors and operators all understood this well as some operators with the less popular arcades tended to set dip-switches on the games [that supported this sort of customization] to provide more lives for the payment.
Of course, the consumer almost always likes to have the benefit of "extra lives" as this equates to more entertainment.  But, for games that are in very high demand (e.g., "Outrun," which imposes time-limits instead of number of lives, when it was new, was a big arcade machine that featured a seat shaped like a car that actually shook and tilted {if I recall correctly} and vibrated in concert with in-game events, for which I've included a few images below), many arcade operators set the dip-switches to severely limit the numbers of lives under the guise of "giving more people a chance to play" (although I suspect that this decision was more likely motivated by profit).
Pinball machines had exactly the same concept, except instead of lives the player got balls.  Typically 3-5 balls per quarter.
One common factor as well was that once all the lives (or cars, or balls, etc.) where lost, the game provided an option to the player to insert another quarter to continue (and get another 3 or 5 lives, cars, balls, etc.).
Measuring skill...
As I alluded to in the comments, having lives can also aid the player in measuring their skill:

What score did I achieve with 1 (or 3, or 5) lives?
How much gold did I get before the evil dragon killed me?
How many times did I play multi-ball mode on that pinball machine in one go?
How many races was I win with just one car?

These can become "bragging rights" amongst a player's friends, especially if there were witnesses.  I can remember back in the 1980s seeing people crowd around player who's been playing a particular game for a long time, and playing it well.  Comments from onlookers would sometimes include "she [that player] is still on her first life and she's already completed seven levels" followed by "damn, I always have trouble with the umber-troll on level three, how did she do that?"
Such measurements can be an important tie into word-of-mouth marketing too.
Player motivation...
The "losing a character's life" factor also adds yet another quality to the gameplay that causes the player to put a little bit more effort into taking care of their character (e.g., feeding it so it doesn't starve to death, avoiding getting hit by weapons, circumventing dangerous traps, etc.).  With the possibility of losing lives, the player will get more emotionally involved in the gameplay sessions which, in turn, makes the game more interesting.
If a character never dies, the game may never end and could become quite boring, at least in the case of an action game.  For games like Chess, Ma-Jiang (incorrectly spelled by most authors as "Mah Jongg" or "Mahjjong" and so on), etc., there obviously is no need to have a concept of "lives," but for most action games where your character is at risk of dying it's beneficial.  Ditto for pinball and other such games too.
Also, if the player makes some serious mistake in the first 10 seconds of gameplay, the additional lives are a wonderful feature.  Not having this feature can be very discouraging, especially for new players.
The player knows that there is a limited number of lives available, and will work toward an unspoken goal to improve their gameplay abilities.  Of course, this will require practice, and so the extra lives are also helpful here too.
Pictures of Outrun...
I've included a few pictures of the Outrun game I mentioned earlier.  For those who remember playing this game in an arcade, I hope this will also bring back some fond memories.
Comment: Financially this makes sense for arcade games. But what about games you don't pay to play, say console games you own? What is the purpose of the life?
Comment: +1 Outrun but call me a tedious bore, however, Outrun is my favourite game (after Elite on BBC B, disk edition) and I do know for a fact that it does not have lives. You have 75 seconds to complete the first stage and you can crash as often as you like, however, crashes take time and you need that time to get to the next stage. The dip switch in the back enabled this initial time period to be set to 90 seconds. Naturally the operator could charge a different amount per game, e.g. 50p a go, 50p for 3 goes with 20p per go in the next slot. With each go you would start at the start with 0 points.
Comment: @Jeff Initially they were carryover from arcade ports and then they were kind of like grandfathered in. Recently though, more and more games are doing away with the concept of lives (like in fable 2+ where you don't die)
Comment: @ʍǝɥʇɐɯ: In looking back at my answer, I see that I didn't make any claim that Outrun has a limit of lives (I was making a point about how games that were in more demand tended to be limited to fewer lives or less time by the arcade operators), but I've updated my answer to clarify that it's time-limit based anyway.  Thanks again.
Comment: The player gets a way to measure their performance -- "how many lives did you achieve before dying?"  Also, there may be a bit of a traditional factor there, or even a hope by the vendor to see the game in a future video arcade.  (I'm adding a little bit more to my answer about motivating players.)
Comment: @Jeff I think its more "following convention" with the first consoles.
Comment: @ʍǝɥʇɐɯ:  Thanks for clarifying those details about Outrun's mechanics (+1 for you).  The idea of a time limit serves a similar purpose, but I'll see if I can update my answer soon to touch on this.
Answer: Finite lives are a form of resource management for the player.
If you notice, most games that have a finite count of lives tend to be very binary about being alive or dead. Maybe the player gets a couple of HP, but if you get hit more than 3 times or so, you lose a life. And there will generally be a healthy supply of "insta-death" lurking around, whether it is pits, spikes, etc.
Because of that, lives function as resources in the same way that healing potions do in RPGs. The more you have, the more likely you are to be able to progress further. You don't have to push as hard, since you have more lives to try again. This is also why RPGs, even historically, almost never used multiple lives. There was no point, since they already had plenty of resource management.
One of the reasons why finite lives is going out of fashion for games these days is that running out of lives generally isn't fun for most players. While the tension created by having low lives is nice, if you ever actually run out, the game becomes a lot less fun. You lose a lot of progress.
One of the other reasons why finite lives aren't used often is because game developers tend to allow you to save anywhere. Or at least, at reasonably-space designated locations. Because of that, the only progress you can lose is back to the last save point. So, unless save points are significantly different from checkpoints, there's really no purpose to it. And if they are significantly different, players may not like that very much.
So the only way to make finite lives worthwhile is to punish the player significantly more for running out of lives than for simply losing a life.
Answer: Its an additional difficulty control.  In addition, it forces replay of the first few levels, which both builds skills and essentially gives the game more play.
Consider a game that was easily beatable in one 3 hour sitting, without "dying" or having to start again.  Probably you would then shelve the game and never play it again.
Or consider also a game that is incredibly difficult and only lets you die once ( vid: Double Dragon III ). You would likely shelve the game and never play it again.

Games that mix the right amount of challenge with the right number of lives produce a lot of fun replay.  One of my favorite games was Battletoads. Replaying the first few levels in 2-player mode is still a lot of fun.

Basically the trade-off between life-meter and now-you-have-to-start-again.  Its nice to not have to start again from the very beginning, which would be too challenging/discouraging and would play-out the first few levels faster.
Besides life you also have to consider continue/password. Password was an early alternative to savegame, but again, all of these are just means by which to control the difficulty of the game and make it winnable, without making the game too dry to keep starting over from world 1-1.
Its interesting to see how different games handled this though.  Take TMNT I, where each turtle only had one life ("getting caught"), but you had 4 turtles, so effectively 4 lives.  (They could be rescued as well, but that was really rare/difficult).
Comment: +1 after reading only the first sentence "it's an additional difficulty control," although I think this entire answer is quite good because it expands logically on that first sentence very nicely.
Answer: Lives are a way of tuning the feedback loop that players engage with the game through (reward/punishment for actions taken toward goals).  A crucial part of gameplay is learning; a game design where punishments of lesser degree than termination of the game are available gives more opportunities for players to learn which behaviors earn rewards and which earn punishments, and so promotes engagement.  Of course there are many ways to accomplish that, but since "death" is a common metaphor for game termination, a natural modification of that metaphor becomes "multiple lives".
Answer: In short. If you are giving player a challenge to get from Point (or objective) A to B and its somewhat long. You may not want to force the player to start over if he makes a mistake but you may want to limit the amount of mistakes he can make by using lives which spawn you at last checkpoint.
In a game like zelda (ocarina of time) if you die you start at the beginning of the level which isnt too much of a big deal. However if you accidentally fall in a hole you wouldn't want to start over again so instead of 'lives' (which you dont get) you get deducted hearts/health points instead which is a fair alternative.
Answer: Games are for playing purpose. Player play the game to win something, to have fun. Every time they fail to do that, they just ask for another chance. They think, this time, this time for sure I am gonna make it. That's the purpose of having life.
Comment: ...and then they get addicted (and insert more quarters...), +1.  =D
Answer: Humans are very risk-averse in terms of death.  When a game designer adds the concept of lives to a game where the character in the game might die, they are essentially encouraging the player to take risks they wouldn't otherwise take.
Further, it helps draw players into the game, where the first time they play they might die with minutes of starting.  Once they start the game, however, they feel the need to continue trying while they still have remaining game time, or lives, left. Ideally they will learn enough during this time period that they will desire to play the game again, even though they may have to start from the beginning again, having lost all their lives.
Comment: @Tetrad There's two ways of interpretting the question.  I started by looking at it the way you are considering it, but it got too lengthy, and quite frankly this way is more interesting.  Games which have no "death" need no lives.  Of games that have death, you either get one chance (no lives) or you get multiple chances (lives). So I'm already assuming that we're discussing games where player mistakes may lead the player to restarting the game and/or a given level.  Therefore adding lives means extending gameplay beyond the first mistake.
Comment: +1 for this answer because it starts to get into psychological factors.  There is a benefit to "not dying" that is hard-wired into our brains which is key to our survival (especially back in the days when we were cavemen, as strongly suspected by scientists working in this field lately), as there is a "reward" we feel from overcoming something that would otherwise be dangerous.  This doesn't necessarily cause us to take risks, but it does require us to take risks more seriously and contributes to problem-solving intelligence development (another important aspect of gaming often overlooked).
Comment: "they are essentially encouraging the player to take risks they wouldn't otherwise take."  Wouldn't it be the other way around?  If you add the concept of lives being removed when you die, wouldn't that mean that you're discouraging risk taking? "Dying is bad, I might die if I do this, therefore I won't."
Answer: It is simple, the purpose of having lives is to allow the player to fail multiple times before total failure or having to restart the game. While games like traditional Arcade games give lives as a means of profit (1 coin, 1 life), the same Arcade games on consoles use lives as a means of trying to get the player to play carefully without having the higher difficulty of permadeath.
In other words: lives are there to help others despite their failures, and as an alternative to permadeath, given that feature's negative aspects. Yet it still retains a form of permadeath (after X lives are lost, you are gone for good!) which retains some of the POSITIVE aspects of that feature.
Answer: Several reasons for lives to exist/not exist:

Limited lives provide an additional challenge, but are clearer than "don't take more than 1000HP" -- which is what they eventually equate to.

In many games, dying provides a delay until you are permitted to revive. This provides both an opportunity for you to regroup and reconsider your approach, as well as for your enemies. In some games, bosses regain their health when you die, in PvP games your teammates might suddenly be outnumbered because you're dead for a few seconds. Death can be a tactical (dis)advantage.
But being dead is boring to a player, so there are also games (Call of Duty: Modern Warfare comes to mind), where, apart from respawning a distance away from the battle and having to run back, you revive immediately. Or WoW where you can run to your corpse immediately instead of waiting to revive, or SWTOR where you can revive in place if you're a subscriber or pay, instead of far away at the med droid.

In classic Arcade games, it was how they made money. You pay for reviving. Some games today also still do this, e.g. you lose credits when you die. This is less harsh, but encourages play on a higher level because you have more spending money left for gear, vanity items etc. OTOH it avoids locking out people who can't afford to pay for revives (e.g. the F2P players you need to keep the game populated so the actual customers - paid players, especially "whales" - can have fun).

The concept of death serves as a fixed cut-off point for player ability. If you die in this level, chances are you haven't mastered an ability you need to build on for higher levels. By making you die, a game can make you aware that you need more practice before you e.g. end up in a PvP session and cost your team a win. It can also just serve as the criterion whether you get to advance in rank in a game, or get rewards.

In short, it depends on what kind of game you are making whether the concept of lives, of penalizing bad performance, makes sense. LucasArts adventures famously don't have the concept of death. You can take hundreds of hours to finish a game, and apart from you maybe losing interest, there is no penaltly. There is no walking off a cliff or otherwise losing. Puzzle games don't have lives. You just don't win until you get it right.

What is the purpose of having lives?