How encouragement design works practically?

Question: I'm trying to understand the encouragement design but I have some doubts. For example, if I want to introduce a voucher for teachers that can be used for professional development(the treatment) and I want to estimate its impact on student performance(dependent variable) obviously I have some problems, since not all the individuals in the treatment group will actually use the voucher. How can I introduce the encouragement design in this case? for example is it right if I send (randomly in the treatment group) some invitations to some professional developments program and I use their participation to these invitations as instrumental variable? And what's the difference with intention to treat?
Comment: a dummy variable with a value of 1 if the teacher used the voucher would be an excellent start.
Answer: The fact that you can only encourage but not force the teachers to participate puts you squarely in the world of Local Average Treatment Effect (LATE) and Intention to Treat analysis.
Essentially if you use the voucher as a instrumental variable, you will get an estimate of the effect of the voucher on "the sort of person who you can encourage to take a class by giving them a voucher".
Read the Instrumental Variables section in Mostly Harmless Economics, to get a good easy to understand explanation of exactly the situation you are interested in.
Comment: If you want to measure the effect of giving the voucher on student performance, then run a regression with a dummy for GotVoucher. Do not include a dummy for whether they used the voucher.
Comment: Running a regression directly using the dummy for whether they took a class will give you incorrect estimates of the casual effect of taking a class on student performance.
Comment: The voucher here is actually the treatment. If I understood correctly if I use the dummy variable suggested by jamzy as the instrument I would be doing an intention to treat analysis. What I don't understand is what happens if I want to also use an encouragement design by giving some invitations to a randomly selected teacher in the treatment group. In this case can I still use the the instrument suggested by jamzy? Actually can I just give the encouragement to all the treatment group?
Comment: If you want to measure the effect of taking a class on student performance, then run an instrumental variables regression using the dummy for Got Voucher as the instrument for whether they took the class.


E-B-G-D-A-E Guitar Strings Vs. E-A-D-G-B-E Guitar Strings?

Question: So I am a super noob to guitar. I play piano mostly. I recently restrung my dad's old classical guitar (nylon string). I am looking at the tabs for a song and the strings are going like "E-B-G-D-A-E" like what is that ? I thought it was E-A-D-G-B-E ?! so confused this is the link btw. Thank you ! http://www.guitaretab.com/j/jung-yong-hwa-of-cn-blue/300154.html
Comment: You are looking at the note names of the strings in both forward and reverse order. 1 through 6, and 6 through 1.
Comment: Imagine: you're holding a guitar playing and you want to look at the strings to make sure your fingers are in the right spot. From this angle the high e is on the top with b under it (second from the top).
Answer: When you hold a guitar the fretboard looks like that:

The thickest string at the bottom and the thinnest at the top. Some people prefer to represent chord diagrams in this way, other people prefer to represent chords as they can see the fretboard in a mirror on the wall. It is only a personal preference.
Comment: Just to be clear : Thickest string nearest ceiling (or your chin), thinnest nearest floor.. bit confusing to call the one nearest the floor the "top" one, but it kind of feels that way when you hold the guitar
Answer: Another way to remember which side is up on a tab staff: just like on a normal staff the higher notes are on top.
Answer: In tab notation the most thin string on guitar (also called the 1st string - in the standard tunning this is the E-first string) is presented on top line and then next strings down to the  6th string - also E in standard tunning on the bottom.
Sometimes you can find different note names next to the tabulature lines, and that means tabulature is written for non standard tuning.
The so called DAGDAD tuning is quite popular, and you can work it out yourself :) which strings should be tuned to which pitch.
Comment: Might be an established practice in some circles, but in others, like rock music, it's a very unusual ordering. Can you specify in which kind of tabs you see this happening all the time?
Answer: Try playing Spanish or Italian baroque tabs.  They put the highest string on the bottom, as though you were looking at the strings in a mirror.  French tabs of the same period are more like modern tab, with the highest string in the top.  Switching from one to the other is a bear!  But I would guess that modern tab just puts the highest string at the top as a way to imitate regular notation.  It's easy to get used to -- higher notes are higher on the staff.


What's the motion of this yoyo under external force will be?

Question: A yoyo on a horizontal table is being pulled by a string to the right, the table is not frictionless. If we only know that the object doesn't slip, how do we know if the string is winding up or unwinding? My reasoning is initially the friction is not ever effect so the force pulling the yoyo to the right will act a torque to the object such that the string is unwinding. But someone else said it should be winding up. I don't know why.
Answer: I think that a sketch says more than equations and words

The yoyo will, in an infinitesimal sense, have to move around the red dot (but is kept from doing so by the table). The direction in which the yoyo will move, depends on the angle of the string, and thus the direction of torque around this touching point.
Answer: If the outside radius is $r_O$ and the inside where the string attaches $r_I$ then the no-slip condition is $v + \omega r_O =0$. The string lengthening rate is $\dot{l} = \omega r_I$ so the end of the string motion is $\dot{x}=v+\dot{l} = v + \omega r_I$. Together they make
$$ v  = \frac{r_O}{r_O-r_I} \dot{x} $$
  $$ \omega = \frac{1}{r_O-r_I} \dot{x} $$
and their derivatives
$$ \dot v  = \frac{r_O}{r_O-r_I} \ddot{x} $$
  $$ \dot \omega = \frac{1}{r_O-r_I} \ddot{x} $$
First if we assume the friction force $F$ acts in the opposite direction as the tension $T$ the equations of motion are
$$ T - F = m \dot{v} $$
  $$ T r_O - F r_I = I \dot{\omega} $$
All of the above are solved for
$$ T = \frac{I+m r_O^2}{I+m r_I r_O} F $$
  $$ \ddot{x} = \frac{(r_O-r_I)^2}{I+m r_I r_O} F $$
This means that if $F$ where to switch signs and work in the same direction as the tesion then the end of the string is going to have a negative acceleration $\ddot{x}<0$ which is impossible because the string would slack.
So the assumption that $F$ acts to the left must be correct.
If we back substitute $\ddot{x}$ into $\dot{v}$ and $\dot{\omega}$ we get an idea which way this thing is going to move
$$ \dot{v} = \frac{r_O (r_O-r_I)}{I+ m r_I r_O} F $$
  $$ \dot{\omega} = \mbox{-} \frac{r_O-r_I}{I + m r_I r_O} F $$
So the center of the yoyo is moving towards the right, and it is spinning clockwise winding the yoyo up.
Comment: How did you include the angle with which the string is pulled? Try with a real yoyo, you can upwind or unwind it, depending on the angle of the string with the horizontal. This is something that you should include in the derivation.
Comment: I thought OP said horizontal (pulled to the right, not right and up).
Comment: It's not my question, but I think the question is a bit lame when only pulling horizontally.


Parshas Zachor Sfardi versus Ashkenazi

Question: Can a Sefardi be Yotzeh Zachor with an Ashkenazi Laining and vice Versa?
Comment: Given that no one discussed having multiple readings for visitors before 100 years ago, clearly there is no Hava Amina it should be a problem.
Answer: Rav Moshe Feinstein writes that all ethnic pronunciations of Hebrew are equally acceptable, even for chalitza which requires the reading of specific Hebrew verses. I'd assume the same would apply here, according to him.
Comment: I have watched a chalitzah with a talmid of Reb MOshe being the Main Dayan and he asked the women which pronunciation she uses and told her to use the one she normally does so I find the Teshuvah intresting
Comment: Where does he write this?
Comment: That way the rabbi knows that what she's saying is correct for her pronunciation, and not a mistake.
Comment: What Shalom is saying is even though Reb Moshe holds that any pronunciation is okay, it still must be consistent to be considered a pronunciation at all. That is why we ask the woman at Halitzah to pronounce it in her normal way.
Comment: He told her to Pronounce it the way she is used to saying it she was an Isreali in America meaning She Spoke regular and with the Isreali Ivrit accent
Answer: My LOR/P told me that I can be yotze with Ashkenazim as long as the reader differentiates between ע and א and between ח and כ (which was the case in my situation).
Answer: Yalkut Yosef (685:12) says Bediavad he is Yose - ומכל מקום אם שומע את קריאת פרשת זכור במבטא אשכנזי, ומתוך ספר תורה בכתב אשכנזי, יצאו ידי חובה.
And also, later on he says an Ashkenazi is also Yose from a Sefaradi.
Answer: My friend had it from R Dovid Feinstein that one should look for a reader with his own havarah. In this case the koreh used Israeli, and my friend used sav and komotz.

Parshas Zachor Sfardi versus Ashkenazi


How do I set up donations with the Donate App?

Question: I have added the donate button to my page, SaveMMJ.  I have not been able to figure out how to allow donations.  I cannot find a way to give my paypal information.  I have tried to donate myself to test it and paypal says there is an error.  Can you please give advice for what to do after adding the app so that people can give to the cause?
Comment: I don't believe Facebook has a 'donate' button, you'll need to clarify what you're talking about
Answer: I assume you're talking about http://www.facebook.com/donateapp?  I have it installed on my page, and you just need to ensure your PayPal account is a Business or Premier level.  I don't think it works on regular accounts, so we upgraded ours (for free) at PayPal.com


Difference between Zero-Crossing Optoisolator and Regular Optoisolator

Question: I am trying to find any documentation on what the purpose is of a Zero-Crossing Circuit TRIAC Optoisolator.  The datasheets don't explain the concept well enough.  If you do answer, please include references or explain how you found out.  Thank you!
Answer: Zero-crossing is typically used for incandescent bulbs. You may have noticed that when incandescent bulbs fail they always fail when they're switched on. That's because the mains phase can be near its maximum when switching on. Combined with the low resistance of a cold bulb this results in a high current peak, which may burn the filament. When you switch on a zero crossing you avoid these peaks.
How I found out? I've known this since my time in college. It simply makes sense.
Comment: Thanks. That makes sense.  Boss says we won't need to worry about noise or spikes in our heater driver circuit since our heater is pretty rugged and the heater's power doesn't have to be perfectly clean.  So I will shop for a non-ZC TRIAC which should be cheaper.
Comment: There is no certainty that a Zero Crossing driver will cost more. Best choice is to list what you want and then look at availability and prices. If a ZC driver is cheaper or about as cheap you may want to us it. A heater will probably not care too much or make much interference but, all things being equal, a ZC driver is usually more benign.
Comment: Not only for incandescent bulbs. Also for always loaded transformers (mono or three phases) which can't be (or are not) disconnected from their loads.
Answer: Zero Crossing refers to the load voltage at which the triac will switch.
Wikipedia has a little information on the theory of Zero Crossing.
Basically, the triac will hold off its switching until the alternating waveform of the load signal crosses the 'zero' or midpoint of the waveform.  This helps alleviate sudden voltage spikes when the switched load jumps from 0V to say 100V in one instant.  By ensuring that the load is only switched when it's waveform is crossing the mid-point, the voltage increase will be a smooth rise from 0 to maximum.
Answer: According to my research, a zero crossing detector is used specifically for protecting a connected load. It does not exactly matter whether it's with a triac or directly with mains. As mentioned in one of the replies above, a load could most vulnerable at the introduction of a sudden peak level of the AC phase during a power switch ON, a zero crossing sensor ensures that the load is always switched ON at the first zero crossing of the applied AC phase, thus safeguarding the load from the dangerous peak levels.
With triacs a zero crossing could be useful for protecting the loads as well as for reducing RF interference.
I have tried to explain the concept comprehensively in the following article
How to Make a Zero Crossing Detector Circuit


Practical implementation of Mathematics

Question: I am 21 years old now. I have been studying Mathematics in school, college and now in university but I simply feel that I don't practically understand it. For example, I can solve complex questions on paper but in real life I can't even add up things properly. Its really embarrassing situation sometimes. I would be very thankful if you all can guide me with some tips what should I do to make my mathematics good.
I don't know if this question really suits here but I did not find a better place for it.
Thanks in advance.
Comment: http://www.phdcomics.com/comics/archive.php?comicid=1356
Comment: What exactly are you worried about? "Making your mathematics good" is a very vague question. Are you worried that the things you have learned still make you... "useless" in some sense? I think what you mean is that you can answer things in a course context, i.e. when you are somehow guided towards a solution by the teacher, but not outside of this context. Am I right?
Comment: @PatrickDaSilva: I simply cant apply it in practical even if it is from course.
Answer: Unless you were following fixed procedures and just blindly plugging in numbers into formulas, you should have a decent understanding of mathematical concepts.
Finding practical uses for what you know is the best way to build up your intuition. For example, a got a good feel for linear algebra by writing OpenGL programs which require use of interpolation and matrices to transform objects.
I suggest that you write down situations where you've felt your math application was inadequate, and then work on practising the math that's applicable to that situation.
Answer: I think that education should be about what you want to do. If you'd like my opinion, I think it would be good to ask yourself why you're studying mathematics in the first place and then decide a course of action from there.
To illustrate my point, I'm a mathematics major at a university. In high school I hated math so much. I swore I'd never sit through a math class, or for that matter, crack another textbook. So I joined the army. Five and a half years later, I hungered for knowledge and wanted to challenge myself. Hence, I got out and went to college.
When I first started school, I took math because it was required and I had to "check the box." But since my mind was open to the pursuit of knowledge -- my GOAL was to learn, not to get A's -- I found math beautiful.
I started off at the university as a double-major in biochemistry and neurobiology. It was interesting for a while, until I realized that the upper-level courses were purely focused on application and the theory was, I guess, missing for me. I decided to switch in my senior year to math. The reason is because I want to learn for the sake of learning. I want to pursue math because I find it beautiful.
So, back to your question. In my opinion, I think you should ask yourself what you want out of mathematics. If you want to be able to apply it to "real-life" situations and you feel that you're somehow lacking in that field, take it from me, all you need to do is practice. I failed high school algebra twice then I went on to the army for five and a half years where the only "math" I did was count how many rounds I had left after a firefight. I came to college, busted my ass, forced myself to get better at it and kept a 4.0 GPA for three and a half years in math. My point is that you can do whatever you put your mind to. All you need to do is work at it.
I'd like to say one more thing. You wrote that you feel you understand complex questions on paper, but in "real life" can't even add properly. To me, mathematics is not about arithmetic or modeling physical phenomena with equations. If that's what you want to use it for, then you can improve with hard work. (Again, trust me on this.) However, if you can solve those "complex questions" on paper and you take satisfaction in that, if you can find beauty in it, then love it for what it is.
Answer: I think one thing you really want to be able to do is quick arithmetic, which can be fun, confidence building (and reduce embarrassment), and is most likely the easiest of your goals to achieve.
There's a lot of books on how to do quick arithmetic, but the most fundamental skill is rote memorization using flash cards before using fancy tricks.  Just make yourself flash cards for multiplication tables 1..12 X 1..12 and addition tables 1..10 + 1..10.  The key is that you have to get to the point where you know the answer right away.  Practice every day and don't stop until the answer is instantaneous.  There has to be no thought and no counting in your head.  Keep practicing to keep this up, and extend the range to 1..10 + 11..20.  Focus on the ones you have trouble with until they are automatic.
Be patient... it may take several months of daily practice to get good.  That's because when you are training your brain for "fast knowledge skill" you are actually growing new neural networks in your brain, and that takes biological time.
You can do it!  It's how the brain works.  You can get good at fast arithmetic!   It just takes time, effort, and repetition.

Practical implementation of Mathematics


Tools or recipe usable by a non-professional to check their Wifi security for common issues?

Question: For many years I've been careful on Wifi. I haven't know how to secure it properly, so it stayed on an isolated NIC of a good router with normal WPA2-PSK and full WAN access but no LAN access at all, and all was safe.
I'm moving to allow some WiFi, at least, into the LAN. I'll be using decent enterprise equipment (nothing that's left un-updated long), and the basic scheme is OpenWRT AP -> managed switch -> pfSense as router/security device (running RADIUS). AAA will include 802.1X + certs, and probably some use of VLANs (to be decided - the AP, switch and router all handle dynamic+private VLANs and the switch handles full IP/port/protocol ACLs as well).  The exact config isn't yet decided, nor are the exact auth methods (cert + PW/other 2F?) or EAP method, but something along those lines.
I'm aware from general reading, of some of the more common warnings that apply to these security methods - validate certificates, don't allow VLAN tags to escape to client devices, generate and keep any self-signed root CA on an airgapped device and use intermediate CA+revocation lists for day to day use...
In theory it should be safe (I'm not at all comfortable with WPA-PSK2 alone as the guardian to my LAN), or certainly a lot safer than most other alternatives, but I like to test my work, not just assume it's done okay, and I'm aware that I'm not a security pro or a WiFi pro. I doubt I could learn enough in less than 5 - 10 years to provide any kind of reassurance by self-testing my WiFi security, though I'd certainly like to be able to do so.
What I would like to ask is - is there a good (automated) way to test if the WiFi is secure or "leaking"? Good security is hard, WiFi harder than most, and I'm not entirely sure I trust myself to test for or spot a weakness, if I hadn't done it right.
So I'd like to have some kind of basic or moderate penetration/vulnerability test approach I can use as a partial make-do.
It won't be the "full thing" because that needs human knowhow, but is there something (anything?) that covers the basics applicable to my scenario, and doesn't need much knowledge  or is automated / "follow a recipe" to use it, and which will let me gain at least some level of reassurance over common WiFi/AAA vulnerabilities.
Update: criteria and definitions
As commented, the question needs a more specific defintion or criteria for "security". Some broad areas are easy to define:

Security aspects: I'm looking at one aspect - the perimeter security, as seen by a WLAN-based user. Not having implemented 802.1X or used VLANs in the context of infrastructure security before, it's easy to get something wrong. I might create a setup/config where I think it's all okay, but to someone with a little knowledge or a standard penetration testing toolkit, it's quickly clear that there's a weakness in the setup that suggests there could be an AAA bypass.
Risk exclusions: I can exclude several broad areas of attack for the purposes of this question, although they are crucially important in the bigger picture and make up some of the most exploited system vulnerabilities in practice. For example:I can exclude most endpoint issues (individual system+software vulnerabilities of the endpoint PCs and servers on the LAN, including PCs/laptops with their own Wifi cards on board), because those need securing/updating as it stands already, and are kept up to date. They are a "known" and unchanged by the proposed network alterations. I can exclude malicious piggybacking via attacks on user's wireless phones/laptops that are subsequently attached (correctly) to the LAN via Wifi. The endpoints already need to be kept up to date and protected as it is, and that's a different issue which I'm familiar with and already do what I can with. Those are important but at least I'm already clear what I need to do and can accomplish on them. I can exclude IOT wifi control issues. I don't have any IOT or wireless possessions other than phones/laptop and if I did, they wouldn't be allowed on the WiFi or LAN other than at most, totally isolated from the LAN at the router via dedicated NIC to reach the WAN only, which I'm comfortable doing. I can exclude egress traffic, monitoring of activity within the LAN interior itself. If they're already inside it's already too late and safeguarding has failed. I can exclude physical access issues (including non-consented connections to wired LAN ports). This is an attacker who has no physical access to the devices themselves, or to existing wired infrastructure. They are not in the house (or even if in the house do not have access to my infrastructure devices/cabling). Wired LAN ports in rooms where guests might visit have to be addressed anyway so this is a "known", and in any case LAN port misuse is a social issue (managing visitors) as much as anything. I'm also not looking at an attacker who has other knowledge beyond what can be gained from a "cold start". For example, the hypothetical attacker has not used social media or social engineering to gain useful knowledge about the system or to build a list of possible passwords, and is not someone previously invited into the house and granted some LAN access, who has an old password or certificate to hand.
Documented weaknesses/vuls affecting wireless/wired infrastructure, access points and AAA (including Wifi APs, LAN networking, FreeRADIUS, and/or other common AAA infrastructure). For example, checking if WPA2-PSK is used and the wifi vulnerable to KRACK, or (hypothetically) suppose that there was a well known weakness in some switches, that caused packets, including those that are superficially AAA related, not to be correctly routed onto the expected VLANs. CSV is included but I'm more concerned about what might be called setup/design/implementation weaknesses than CSV since CSV can mostly be handled by update management as far as anyone can manage it.
Implementation flaws/weaknesses, including "well known" infrastructural/design issues/flaws and common config flaws/weaknesses/oversights are very definitely included. This includes issues caused by common misconfiguration/exploitable configuration weaknesses - what one might broadly call implementation issues/weaknesses.  (Without narrowing it down, examples off the top of my head might include, the user has forgotten to configure AAA to validate certs, or has accidentally connected their VLANs in a way that one seems to be able to reach IPs that don't seem to be the correct AAA devices,  and might be endpoints or unintended interfaces rather than the correct AAA systems, or is using known-weak algorithm choices.) To an extent, this is almost the primary issue
Hypothetical attacker's motive + skillset: My hypothetical attacker is not a hardened targeting attacker (NSA or someone determined to break into this specific system with a high level of skill/resources), but isn't a flyby or clueless "road warrior/botnet script kiddie" either. They have some moderate but non-InfoSec-professional-level skill (vague I know!) and some interest in penetrating this system, but will leave off fairly readily if it's clearly not going anywhere and there's no obvious way in, after a while of trying. They are comfortable throwing quite a range of usual/automated probes/toolkits/scripts/sniffers at the system, to see if RADIUS authentication can be bypassed or fooled, the trusted vs. untrusted VLANs jumped across, ACLs accidentally allow connection to localhost or other IPs they shouldn't, an SSID/BSID has been left incompletely or unsafely configured, the certificates can somehow be leveraged, some kind of chink left which allows them ingress, or whether there's a classical misconfiguration or failure to do something that would be a green light to a penetration tester, and which signals that there's good reason to believe the perimeter can be breached with a bit of work.

Put another way, the hypothetical attacker will throw a fairly broad or decent subset of decent automated penetration testing toolkits at the wifi from a nearby house or car, and sniff the airwaves for network traffic, and see if any of this pops up a "you have a vulnerability" message that might signal a way in past AAA and make it worth further attention. (They have the basic knowhow to do this, but not the knowhow or motivation to spend weeks crafting a targeted attack or putting endless resources into this one system.)
They might also try exploring whatever aspects of the LAN AAA setup are exposed by the wifi or its clients, to see what information can be gathered and see if any of that suggests it's weak. If a weakness arises then the wifi gets more attention, if after a while of trying, still nothing obvious is evident, then they will finally move on.
What I'm looking for, then, is almost the flip side of this:
As a non-professional without specialist experience in InfoSec tools and lacking a lot of the experience people might take for granted on *nix platforms, there will be a natural limit to what I can accomplish in the way of self-assurance. I'd expect to be good at interpreting output, but I might not know enough to use the in-depth tools and CLI approaches a pro would use. A toolkit (or more than one) would help.
Essentially it's the same difference as using CLI and knowing what packets to craft, or probing using Kali, vs. using nmap, if probing a network and its ports. For a security non-pro, nmap's automated scans and their options offer a fairly comprehensive starting point for a range of useful device scanning, and will covers a lot of ground in depth (exposures and what they might reveal of the device) which they wouldn't really be able to obtain without it. Whereas Kali would not be a good choice - it's much more powerful but requires much more in-depth knowledge, as a professional's tool of choice.
I imagine that when a professional does a non-physical penetration test, the starting point is a bunch of tools used to gather information about the LAN and its Wifi, how AAA is set up, any SSID names/IPs/package info/other information that is straightforward to gather, port scans, known CVE issues detectable/exploitable from outside, and so on. I imagine that the toolkits available can test for a wide range of information and known weaknesses, and a pen tester will use these as a time saving starting point for their work (their time is valuable). An attacker using these might see there is nothing obvious, or see something reported that suggests there is benefit in attacking further.
So the flip side is, what tools, toolkits, or combination of toolkits, could I as a non-pro use, to essentially probe my own WLAN and get a useful and moderately comprehensive sense of whether its wifi boundary and AAA setup (including those parts of the LAN which provide AAA services or carry/route untrusted pre-auth traffic if any) has such vulnerabilities, and (if so) what they are? Are there tools/toolkits designed for penetration testing, that I might find accessible and which will tell me if a pro would find a suggestive evidence from automated tools, that indicates an AAA/WLAN weakness?
I'm fairly sure I could interpret tool output - that shouldn't be a problem - and I'm comfortable learning enough to run a range of tools, but some tools may require a depth of knowledge and interpretation to use in the first place, to such a point that they aren't really usable other than by security pros (I might not get the appropriate information from them becaue I didn't really understand how to configure the tool for use or they needed considerable human input to guide their use), compared to others that might be quite capable and comprehensive but not need quite the same depth of knowhow to be operated.
If more is needed, let me know.
Comment: @YLearn  He does say against any common wifi/aaa vulnerability.  Could be defined as any wifi exploit that has a CVE entry.
Comment: When it comes to a number of things, including networking, the important part of calling something "secure" is really about the definition. If you want a perfectly secure PC, disconnect it from everything, put it in a lead box, encase the box in 10' of concrete and bury it 100' underground. That PC won't be hacked, can't be exploited and won't leak any information. But it also won't be usable, and usability and security are typically at odds with each other. The issue with asking "if the WiFi is secure" is that we don't know your definition of secure. Your secure may not be my secure.
Comment: @cybernard, could be. Could also be defined under any other set of requirements. The point is without the OP telling us what the security requirements are for the environment, there is no way someone can provide an answer that answers the OP's specific question.
Comment: See update above, and thank you both for the helpful comments and positive approach. I've tried to be specific. Let me know if more is needed.
Comment: When it comes down to it, a bunch of radio waves whizzing back and forth don't have a vulnerability.  It's the endpoints that have the vulnerabilities.
Comment: By "endpoints" I'm meaning the end-user devices (PCs, file servers) as opposed to the infrastructure (AP, router, USM, switches), if that helps. Its the wifi+AAA infrastructure I'd be adding, rather than users' own devices, file servers, IOT and physical network/device access, that I'm considering for risks, and the risks I'm looking at are those accessible to a WLAN-using opponent. If that's unhelpful terminology please say - I'll edit the Q.
Comment: https://security.stackexchange.com/questions/20219/preventing-deauthentication-attacks#20226 This answer is pretty comprehensive (and contains further links), but it doesn't include a note about preventing de-auth attacks via router firmware. Cisco Meraki, for example, have a facility to detect deauthentication attacks, and ignore those packets. Other manufacturers also.
Answer: Based on your question, and the thoroughness of it, I'd say you're actually pretty safe.
You seem to already be doing everything you should be, and most drive-by hackers will see Enterprise Level WPA2, and move on to your neighbor who doesn't have that.
That being said, if you want to see what they see, I'd boot into a Live CD of Kali Linux, and follow some WiFi hacking guides to see if YOU can hack your own WiFi. I know you mentioned Kali as being beyond what you're comfortable with, but based on your question, and what you've already done, I think that you'll be OK. And there are may guides that have step-by-step instructions.
You can also check your neighbors' WiFi to see if they would end up being a better target for would be hackers, (I shouldn't have to say this, but don't hack them.) low hanging fruit that is not you, is a very good deterrent.
You can also monitor your logs (for example, you could find a guide to setup an automatic email when someone connects to your WiFi. You are using pfSense after all), and if a WiFi level breach does happen, you can probably shut it down before they breach your firewall. (If they're even interested in that once they get internet access.)
Again, I wouldn't worry too much. You seem to have a better grasp of security than the average person, and you're doing all the right things.


What is the best way to purchase Bitcoins quickly?

Question: What is the best way to purchase Bitcoins quickly? I don't want to wait a month.
Comment: Depends on your location...........
Answer: On LocalBitcoins.com you can get bitcoins bought under one hour. Just pick a trader who has good reputation (not a scammer) and low response times.
Answer: There's lots of information available here: How do you obtain bitcoins?
coinbase.com has a pretty good reputation I understand, and I find the interface to be quite cleverly designed.
Answer: Check out bitinstant.com
You can deposit cash and get btc sent to your email or btc address right after you pay.
Answer: It really is all about your location. In some countries, it's harder to get set up to sell bitcoins than other countries.
If you're in the UK, try one of these to get near-instant Bitcoins:

Bittylicious
BitBargain
Local Bitcoins (UK)
Answer: I recommend Coinbase. That's how I got my first 10 coins.
When I wanted to get my first coins I was already registered on Gox but wasn't sure how long international transfers would take.
I signed up with them and did the bank deposit verification method. I believe I verified the next day and bought 10 coins. I got the coins immediately but for anti-fraud measures I couldn't spend them for a few days (looks like on 8/20 the wait is 4 business days)
After being more trusted the buy limit goes up and your coins are available immediately.
Answer: If you live in the Netherlands, you can use bitonic.nl to purchase Bitcoins via iDEAL. You get them in a few minutes.
Answer: If you're in the UK then check out https://bit121.co.uk as they are a legitimate exchange with UK based banking. Most bank transfers within the UK are usually instant and you don't have to pay the higher fees when dealing with foreign banks.
Answer: Probably Ebay....From a trusted seller   via bank transfer
Answer: Bitcoin is definitely in its infancy.  I have bank accounts all over the world in USD, GBP, and CHF.  I have accounts on Coinbase, BTC-e, CampBX, Mt. Gox, Bitstamp, LocalBitcoins, and others.
Yet, it is next to impossible to move fiat currency to these exchanges.  In fact, I have only ever been able to buy bitcoins on Localbitcoins, thanks to the immediate transfer facility in the U.K. banking system.
For people who want to buy in USD, which is where the major exchange volumes are, there has not been a way to transfer USD to an exchange without a currency exchange, bank and exchange fees, and a long wait.
CampBX is adding ACH transfer on November 20.
Coinbase not only requires all bank and credit cards to be based in the U.S., they also require the holder to be based in the U.S.  This essentially restricts Coinbase to the 4% of the world that lives in the U.S.
It is frustrating watching the volatile price action and being unable to trade because I can't get fiat to the exchanges.
Comment: you describe the problem, why the question is interesting istead of answering the question.
Comment: The answer depends on where one lives, what you regard as an acceptable transaction cost, what currency you want to buy in, as well as other variables.   Given the unclear question, my comment is as close to an answer as you can get.
Comment: So, you are saying, the question couldn't be answered that's why you wrote something other than an answer? ;)
Comment: You have a point.  I would have (and should have) commented and asked the poster to define the question in a way that one could frame an answer.  However, again, I do not have sufficient points to do this, so I gave some general feedback that might be of interest.
Comment: I think you can always flag posts, here if you come to the conclusion that the question is bad you may use "unclear what you are asking" or "too broad". In this case "off-topic" would also be appropriate.
Comment: With 17 points, I can't do anything.
Comment: I am sorry, not everyone, but with 15 points you can flag. ;)


Benefits of using MacBook Pro with discrete graphics

Question: I'm trying to choose between MacBookPro Late 2013 with discrete graphics card and MacBookPro Mid 2014 with integrated graphics. Judging from GPU benchmark GeForce GT650M has a minor performance advantage upon Intel Iris Pro. Also Late 2013 Model has 2,3 GHz comparing to 2,2 GHz on Mid 2014. The problem is a cost: at my location i can buy this Mid 2014 model for 2300$ and Late 2013 one for 2650$.
My question is: are there any less or more significant benefits of having MacBookPro with this discrete video? I'm ready to pay this 350$ but i don't think 5% of graphics performance worth it.
Answer: You already have the answer to your question.
As far as I see it, the dGPU will be only beneficial for demanding games, heavy 3D work...
If you're planning on using Solidworks, Maya, Lightwave, or any 3d creation or CAD application get the Iris pro one. It is significantly faster for those tasks and not that far behind the GT650M-750M for gaming
The iGPU, will reduces the complexity of your system. Eliminates the graphics mode switching. Less power consumption, prolongs the battery life.
On the math side:
 $2300 vs $2650 is 8.6% or $350.
What can you do with $350?
Buy some software (Games) you always wanted.
Buy USB stick, or External Drive for back ups.
Keep it for rainy days :)
On the other side:
The $350 is not for the GeForce GT650M alone. Check the system specs in more details to find the differences you care about.
My vote would be for the iGPU since it comes with newer model that brings other engineering improvements with it.
Comment: Is 'photo rendering' done on the discrete card?
Comment: I like the point of lower power consumption. Seems that the integrated one would be the best choice for me. Thanks.
Answer: The other thing to think about is that you can't tell OSX not to switch to the discrete graphics when a program that would use it is started, and this can also have a hit on the amount of time you get on a battery charge.
Is that also worth a few percentage points of graphics performance?
If you regularly play graphics-intensive games while plugged into the wall then it probably is. Otherwise it may well not be.
Answer: Definitely go integrated only. Not to save money but to reduce fan noise. Instapaper founder Marco Arment bought a MacBook Pro with discrete GPU back in 2011. He ended up returning it for a model with a much less capable GPU and considerably lower noise.

The 2.0 GHz, 6490M-equipped replacement model does indeed run much cooler than the 2.3 GHz with the 6750M that I returned. The 2.0 has far less fan noise under normal usage, with the fans only spinning up audibly when the CPUs are under a sustained moderate to heavy load.

The Retina MBP with discrete GPU has similar heat and noise issues.
Less famous Alec Kinnear bought the same MBP in 2011. Someone had brought the MBP to me overseas so I couldn't exchange mine as easily and kept it. Years later I'm still not able to use this computer with the discrete GPU turned on (it's too hot and loud) or with external monitor. I can only use it as a carry around thanks to Cory Krieger's donation-ware gfxCardStatus which enables me to run integrated GPU only.
My girlfriend's 2013 Retina MBP 13" with integrated GPU only on the other hand is quiet. I recommend you save your money and your nerves and keep the hot discrete GPU out of your next MBP.
Comment: Thanks for living examples. For the last two years, i've used tons of MBPs with integrated GPUs - i have to say, there was no time i wanted it to be discrete. So, very specific need is to appear to overpay and buy more powerful one
Comment: If you're not gaming Petro, the integrated GPU's are fine. My girlfriend has never complained about graphic performance and she's using every kind of video playback in the world (html5, flash, divx, mp4) as well as doing photo editing. I'm surprised to be writing this as I used to be a dedicated GPU snob. The old Intel integrated GPU's were fairly awful. The old dedicated mobile GPU's didn't used to be as powerful or as heat generating. The nVidia 8600m on the 2008 MBP 17" from which I'm typing now runs reasonably cool even under moderate processor load.


Which engines are Jet-A used in?

Question: Is Jet-A used in turbojets or is it just used in turbofans, turboprops, and the SMA SR305-230 for Cessna?
Comment: Why do you think there should be difference between turbojet and turbofan? They are almost the same.
Comment: I thought the military might use something different because power is better than efficiency in that line of work.
Comment: Most military aircraft have turbofans as well. Including fighters. True turbojets are extremely rare these days. Plus for military having just one stock to supply is much bigger asset than any gain in performance specially tuned fuel could bring.
Answer: Jet-A is mostly for turbine engines in general. Turbine engines can be fueled with nearly anything that you can spray over an open flame and will burn.
It is not a substitute for avgas, for the same reasons that diesel is not a substitute for petrol. You can fuel a diesel engine with Jet-A under some circumstances.
Comment: "Turbine engines can be fueled with nearly anything that you can spray over an open flame and will burn."  With one partial exception - they generally don't take well to fuels with solid combustion products (since these deposit on the turbine blades and do bad things to the engine), unless the engine burns hot enough to keep the exhaust temperature above their vaporisation point until well past the outlet.
Comment: Normal diesel engine won't run very well with Jet-A1, but it is possible to build one for use with Jet-A1 (or any other specific jet fuel type, but Jet-A1 is most common in Europe) and such engines are used on some new aircraft especially since avgas is heavily taxed in Europe.
Answer: Jet-A/A1 is used by pretty much all civilian turbine aircraft. The US military use JP-8 which is similar but with extra additives in pretty much all their aircraft.
The fuels can also be used in suitably designed diesel engines. AIUI the US military runs pretty much all it's vehicles off JP-8 and some airports use Jet-A/A1 for their ground vehicles. In both cases the motivation is simplified fuel handling.
Due to cost/availability/environmental concerns with avgas there has been a push to develop aviation diesel engines that run on jet A/A1 (and in some cases can also run on automotive Diesel). However the GA market is relatively small, certification costs are high and making a Diesel engine light and reliable enough for aircraft use is not easy. So-far only a small proportion of piston aircraft have Diesel engine options available.

Which engines are Jet-A used in?


Why doesn't Barney wear the Duckie Tie?

Question: In How I Met Your Mother Barney loses the Duckie Tie bet in October 2011 when he cannot perform the Benihana routine satisfactorily. He was to wear it for 1 year, hence October 2012. However, I was catching reruns of the episodes and saw the Broath episode, where he was not wearing it, though it would have been well inside the duckie tie year. There are two possible causes: Broath was one of Ted's memories outside the duckie tie year, and just broadcast here OR the bet was invalidated some time later. Anyone know?
Answer: There's an episode earlier in that season (before the "Broath" episode) where Barney is going to have dinner with Nora's parents, but he doesn't want to wear the tie.  He exchanges 3 slaps to get rid of the tie.  The episode is called "Disaster Averted".
http://en.wikipedia.org/wiki/Disaster_Averted
Comment: I edited to make it a little clearer that the answer refers to an episode prior to The Broath.
Comment: And he never goes inside for the dinner, right? Bad exchange.
Comment: Well, the dinner was in a later episode.  Don't wanna give too many spoilers, but he did go to the dinner.
Comment: Good call.  I was in the middle of doing that myself. :D  Thanks.
Answer: This is a real late answer, but the broath is about Quinn, which is the season after Nora. In Disaster Averted they make a deal about the Ducky Tie where he trades more slaps to take it off before meeting Nora's parents.

Why doesn't Barney wear the Duckie Tie?


Lost my private keys and Json or keystore file

Question: I made an account on Ether wallet and I lost my private keys and Json or keystore file. I only have Public keys. Is there any ways to recover my account?
Comment: Related: https://ethereum.stackexchange.com/questions/16785/i-accidentally-lost-the-key-to-my-wallet
Answer:
I lost my private keys and Json or keystore file.

If you've lost your  keystore you won't be able to recover your account.
The public key is generated from the private key, and then encrypted into a json (keystore) file with your passphrase and something called salt, which is a randomly generated value.
Without the json (keystore) file, it's gone.
Private key derives public key which derives address.
In the case of Etheruem Wallet, the private key is encrypted with password and stored in an extensionless keystore file (JSON format, but no extension) with some additional data.

I only have Public keys.

To get the actual private key and do anything you have to decrypt it with your password. If you just have your password, you have nothing to decrypt.
Comment: I saved all files in my USB and it got corrupted. Its not detecting on the computer. Also, I deleted all the files from the laptop. I tried recovering files from the laptop but nothing recovered.
Comment: @Harinder if you've any copy, includes the corrupted flash drive, you have a chance to recover files by use some of recover soft. For e.g. https://www.piriform.com/recuva
Answer: You say that you made an account on "Ether wallet".  Do you mean "MyEtherWallet"?  If that's the case, after you created your wallet MyEtherWallet prompted you to save your Keystore file.  So, there's a good chance that your Keystore file is stored somewhere on the computer that you used to create the account.  You can search that computer's hard drive for files that begin with "UTC-".
Much more information here in the section called "Find Your Keystore File".


What would happen if someone took an oath on a persons grave and lied?

Question: My friend recently took an oath on her dead grandmother an later we discovered she was lying; I want to know what would happen?
Comment: What would happen to who? The friend or her late grandmother?
Answer: bismillah
assalaamu 3alaykum wa ra7matullahi wa barakaatuh
I do not know whether your question is related to someone taking an oat by the grave of someone ( i.e. saying: By the grave of my grandmother I will do this and this... ) or if you ask when someone gave an oath to someone before the person died. But I will in shaa Allah answer on both issues and you see whether the answer suffices you, else in shaa Allah clarify it more.
Swearing by anything other than Allah is not permissible. Rather the oath should be by Allah alone, may He be glorified and exalted, because it is proven that the Messenger of Allah (blessings and peace of Allah be upon him) said:

"Whoever swears an oath, let him not swear by anything except by
  Allah, or else let him remain silent."

and he also said:

"Whoever swears by anything other than Allah has associated something
  with Him (shirk)."

so it is not permissabe to make an oath by other than Allah. If someone made any such oath then this is not an oath since it is haram to make such oaths.
Regarding the second issue I mentioned that someone makes an oath to someone before the person dies there are 2 issues:
1) is the action the person swore to do halal or haram ( if it is haram then there is no oath because you can not do something against Allah )
2) what to do in case of making an oath and breaking it ( based on actions that are halal )
The first situation is clear because you can not go against Allah 'azza wa jalla and one should never make an oath like this, for example: by Allah if you do not give me this I will not do my salah, this is a sin and should be left
The second situation is something else,

al-Bukhaari (6718) and Muslim (1649) report from Abu Moosa al-Ash'ari
  (may Allah be pleased with him), according to which the Prophet
  (blessings and peace of Allah be upon him) said: "By Allaah, if Allaah
  wills, I do not swear an oath then see something better than that, but
  I expiate my oath and do that which is better."
Muslim (1650) narrated that Abu Hurayrah (may Allah be pleased with
  him) said: The Messenger of Allah (blessings and peace of Allah be
  upon him) said: "Whoever swears an oath then sees that something else
  is better than it, let him do that and offer expiation for his oath."

The expiation for breaking an oath is to set free a slave, or to feed or clothe ten poor persons. Whoever cannot do any of those things should fast for three days, because Allaah says:

"Allaah will not punish you for what is unintentional in your oaths,
  but He will punish you for your deliberate oaths; for its expiation (a
  deliberate oath) feed ten Masaakeen (poor persons), on a scale of the
  average of that with which you feed your own families, or clothe them
  or manumit a slave. But whosoever cannot afford (that), then he should
  fast for three days. That is the expiation for the oaths when you have
  sworn. And protect your oaths (i.e. do not swear much). Thus Allaah
  makes clear to you His Ayaat (proofs, evidences, verses, lessons,
  signs, revelations, etc.) that you may be grateful"
[al-Maa'idah 5:89]

If the person does not care about it then the person has comitted a sin and should repent to Allah and make the expiation for breaking valid oath and if the person doesn't do any of these then 'everyone will have what they have earned'.
I hope this clarified a few things in shaa Allah wa Allahu ta3aalaa a3lam
Baarak Allah feekum
Comment: This is a good answer, welcome to the site once again!


Can you join two lists with a user/person column and display in a DVWP?

Question: I have two lists created in WSS 3.0:
1) User details - A custom list (person, supervisor etc) as I can't gain access to the User Information list and can't get XML Web Services to work.
2) Training details - A custom list of trainee, trainer and procedure.
I want to show the details of both lists in a dataview by joining via the trainee/person columns (these are people/group with presence columns limited to people and single entry).  I'm using SharePoint Designer 2007.  When I insert the "joined subview" data into the DVWP I get "No matching items found".
I have no XSL knowledge but believe the following code is probably what's being produced.
<xsl:variable name="Rows" select="../../../Courses_Attended/Rows/Row[@Attendee=$dvt_ParentRow/@Person]" />

I think the problem is that I need the User ID information from what's returned but don't know how to filter that out.
I can get this to work with text columns (i.e. enter the user information as a text field) but I wanted to keep the option of clicking on the user name for details.
Any assistance would be appreciated.
Answer: You'd want to do something like:
<xsl:variable name="Rows" select="../../../Courses_Attended/Rows/Row[substring-before(substring-after(@Attendee, 'ID='), '"')=$dvt_ParentRow/substring-before(substring-after(@Person, 'ID='), '"')]" />


Converting lookup relationship into master detail relationship

Question: I had converted lookup relationship into master detail for a child object which contains lakhs of records. So when a parent record is deleted, all these child records has to be deleted automatically since now the relation has been converted into master-detail. Will this standard deletion throws some error since the records size is huge?
Answer: You should be fine with standard deletes as long as your data doesn't qualify to be a data skew.

Even when you talk about data skew you see the issues mainly around
  updates because of high chance of locking issues but not on deletes.

As a best practice, don't exceed 10,000 child records for a master-detail relationship. Also read Considerations for Relationships
Comment: @MohithShrivastava True let me highlight that part.
Comment: Data skew won't impact deletion capability .It's good practice to ensure data skew is not violated however for deletion it should not matter as the deletion happens under the hood .
Answer: If you have already done conversion ,the child records will be auto deleted upon parent record deletion.Look for if you have any triggers on the deletion of parent record as that could impact deletion.
Below are some of the considerations that one should consider before changing relationship from lookup to master detail

Make sure that every child records has a parent assigned .If you have records with no parents assigned the conversion will fail
All child records will have the ownerId as that of parent and the sharing settings will be inherited of the Parents .
Make sure you don't have reports referencing the field.If you have then those have to recreated as they might throw error .

In short it does not matter how many records you have ,the system automatically takes care of conversion , however be sure to review the implications listed above and first make these changes in sandbox and experiment before doing this change in PROD environment .
Comment: Enhanced the answer to make it appropriate
Comment: OP was asking about cascading deletion after conversion!
Answer: Along with the points mentioned in other answers, find additional notes

Verify if owner field has been used in any classes as detail record of MD relationship should not have owner field.
For huge number of records, there could be possibility of halting or locking the sharing settings, when you change it. So, this needs to be performed outside of business hours.
There could be change in custom report types.

Also, for more information, refer Considerations for Relationships


How to add scale text in QGIS

Question: I'm using QGIS 2.18.4, I wanted to add "scale text" but can't find the tool for adding the scale text on the composer. I only see an option of add text and not "scale text" as in other GIS Software like ArcGIS. Is there anyone who knows this?
Comment: You dont know what you want. Who need scaled text? Try with font size.
Answer: If you want to add a numeric scale like 1:10000 you can add a normal scalebar first and then change the style to 'Numeric' under Item Properties > Main Properties of the scalebar element.
Answer: You can register expression function to get your map scale. For example:
from qgis.utils import iface

@qgsfunction(args='auto', group='Custom')
def get_composer_map_scale(comp_window_title, feature, parent):
    composer_views = iface.activeComposers()
    my_composition = None
    for view in composer_views:
        if view.window().windowTitle() == comp_window_title:
            my_composition = view.composition()
            break
    if my_composition is not None:
        # adjust map id below if you have more maps in the composer
        comp_map = my_composition.getComposerMapById(0)
        scale = '{:.0f}'.format(round(comp_map.scale(), 0))
        return scale
    else:
        return 'Unknown'

And use it in your HTML box or label:
Scale 1:[%get_composer_map_scale( 'Composer 1' )%]

where 'Composer 1' is your composer title.
Answer: In QGis 3.x you can add variables in text item with something like [%'1 : '  || round(map_get(item_variables('Main'), 'map_scale'),0)%]
Comment: Thanks for posting an updated information. Unfortunatly its not working. Does someone know which function queries the live map scale?
Comment: I have tested, it works. You have to remplace "Main" with the name of your map (you find this information in the field "Item ID - id". You can also add a scalebar and choose the style "numeric"
Comment: Thanks a lot. You kinda opened a whole new world to me there. Will give the variables closer attention now :)
Answer: Same as these?:

Integrating numeric scales into a text or HTML box in QGIS print
composer
Is it possible in QGIS print composer to include a
numeric scale in an html box?

According to OSGEO - QGIS developer it is not possible, but it will be in version 3.0. GitHub commit.

How to add scale text in QGIS


Did Palpatine know immediately when the Death Star was destroyed?

Question: I once read on starwars.com before it was taken down, that Emperor Palpatine sensed the destruction of the Death Star as a ripple in the Force. He also knew that Luke (Anakin's son) was the one who did it. Is that true?
Comment: I would think so. The killing of a large number of people does create a sizable ripple in the Force.
Answer: There were over 1 million people on the Death Star when it blew up.  When that many people are killed at one time it can definitely be felt as a ripple in the Force especially to someone as sensitive as Darth Sidious.  He probably also felt the rage of his Apprentice as he watched helplessly from space as rebels destroyed the Empire's greatest weapon.  He would not have "known" it was the Death Star but knowing the battle is happening I am certain he would have made that conclusion.
I never read or seen anything that would make me believe that Sidious would have known who it was that destroyed the Death Star immediately.  However, Luke became very famous throughout the Empire following the Battle of Yavin.  I suspect it did not take long for the Empire's intelligence agents to learn the name of the rebel pilot responsible.
Comment: When Alderaan was destroyed, Kenobi know immediately that something horrible had just happened. I would assume that no matter if you're a Jedi or a Sith, a force sensitive individual would be able to fell this ripple in the force.
Comment: And when Exiled Jedi (protagonist from KotOR 2) caused destruction of Malachor V, she was cut off from the Force.
Answer: I'd say: Not necessarily. First of all, I don't know whether there's been some established "maximum distance" where you could feel such a ripple in a reasonable way. Would it be unlimited, there could be quite some "noise" due to planets getting destroyed by meteor impacts, ships blowing up, etc.
But even ignoring this fact, there's still the question, whether he'd be able to differentiate between the Death Star blowing up or its target blowing up (especially while anticipating the latter). After all there were probably more sentient life forms on the surface than just a few rebels.


Converting 3x7 to a 1x7. Is it possible with only existing parts?

Question: I own a 2000 model Specialized Ground Control full suspension. The front derailleur is rusty and temperamental so my solution is to remove it as well as 2 chain rings (they are removable on mine) and convert to a 1x7. This bike is not worth high spendings on upgrades so would this work if I just bought a 1x drivetrain specific chain ring and kept everything else stock? Better yet would it even work on the current middle size chain ring with maybe a chain guide attached to keep it held on? If spacers are required that's all good. I am only a novice MTB rider and the bike will predominantly be used for downhill and small jumps, no hectic double blacks or anything. I am aware that 1x7 isn't very versatile but it will be plenty for me to have fun.
Answer: You have a zero cost solution, which is to keep the front derailleur but remove the cable (and shifter if you like). Then use the FD limit screws to fix it in the right position to act as a chain guide.
You don't need a 1x chainring, in fact using one with a 7 speed chain is probably less than ideal, so you're actually better off sticking with an existing chainring. You may not be able to get rid of the big chainring, or you may need to get shorter chainring bolts if you do, depending on how the big and middle rings are mounted.
Comment: @Criggie I reckon they will.  the reason for keeping the big ring is as a spacer to use existing bolts, or in some case a mount for the middle ring
Comment: OP may find that sticking with the middle ring might provide enough gearing range for their normal use.
Answer: If the chainrings are in good order, I would recommend servicing the front derailleur and continue to run it as 3x.  The reason is that front dérailleurs rust quickly but are often chrome plated and it's actually easy to remove the rust.  If the derailleur is temperamental it is typically solved by replacing the shifter inner cable ($1 on eBay) and readjusting the limit screws.
Yes it will take up some of your time, but it would cost close to nothing and you will probably appreciate the wider gearing on some occasions.  Also, as noted by others, you'll still need the front derailleur as a chain guide so you would still see the rusty thing if you would run 1x.
Answer: Yes, it's doable. You'll have terrible gear ratio range but you realize this and don't mind.
Either find a narrow-wide chainring that fits the crank, or leave the middle ring in place. You may need shorter chainring bolts as the existing ones have to be long enough to go through the middle and large rings.
You can remove the shifter but leave the front derailleur in place to act as a chain guide, if you can wind out the lower limit enough or otherwise fix it over the middle ring.
Answer: I've done this, converting a bike from 2x11 to 1x11.    I removed the big ring, front derailleur, and the shift cable.
I did need parts, but only shorter chainring bolts.  If you don't want to do that, you could leave the big ring in place, or rig some kind of shim or spacer.
I did run into one problem, which was that the chain dropped off the chainring several times an hour.  There are many gadgets on the market which try to prevent dropped chains.  I ended up getting one of them (a chain guide), and I'm quite happy with the bike.  But if you want a minimum-cost solution, Chris H's suggestion -- to use the front derailleur as a guide and adjust the limit screws to position it -- sounds good to me.
Comment: @stefs Dan uses the original chainring, which is designed to easily let go of the chain for better shifting. You likely have a narrow-wide chainring designed to retain the chain (as no shifting is necessary). And Dan might be riding MTB trails that are rougher than your gravel roads.
Comment: Very helpful everyone, answered all my questions. I reckon I'll try initially with the front derailleur left in place as a chain guide and find out as I go if I need shorter bolts or whether I can fashion a suitable spacer. Cheers everyone!
Comment: why is a chain guide even necessary in this case? i have a 1x11 on my gravel bike, no chain guide and the chain has never dropped off even on rough gravel, forest paths and even short mtb trail passages. Are the chain rings different?
Answer: I run a small bicycle hobby shop.  I have been doing 21 to 7, and 24 to 8 conversions for as long as I can remember.
The conversion can even be done with a riveted crankset that has no bolts in it.  I carefully drill out the rivets or spot weld that hold the 3 chainrings together, throw away the big and small ring, and keep the middle ring.  Typically in these one piece setups the crank arm is fastened to the middle in 9 out of 10 cases.
Then remove the front derailleur, shifter and cable.  I remove between 4 to 8 links from the chain.  I have never had any one complain about their chains jumping off the front sprocket.  Sometimes I will change the bottom bracket to improve chainline.  This conversion has been fool proof for me and my customers.
Answer: I have done it too. 3x7 to a 1x7 added a small chain guide just incase. I feel the chain could be tighter but not sure to just buy a new chain(not sure which is best size for the set up) as upgrading a lot anyway or remove a few links but how many??
Comment: Hi, welcome to bicycles!  It's great that you got this to work; any additional details you can add about how the bike was originally set up and the changes you made would be useful.  What did you use for a chain guide?  Did you need to adjust the chain line?
Comment: Please increase the relevance with [edit]  Note that the question is "can the conversion be done with only existing parts?" so your answer is that a chain keeper needs adding ?  The parts about chain sizing are a separate question, and you can search the website for existing questions about sizing a chain.
Answer: Not a problem, just remove the front derailleur. If you leave all of the chainrings on the crank, you can change the gear range manually depending on how much gear you want for a particular ride.
Comment: This is just [Dan's answer](https://bicycles.stackexchange.com/a/62586/13174), minus all the detail and minus the significant warning that the chain will just fall off all the time.


Configure Modem for Bittorrent downloads

Question: How can I configure the Modem to get maximum download speed for Bit torrents?
Answer: If you talking about dial up modems then, there is no special configuration that will help you achieve greater speeds. Your p2p speed will depend on overall connection speed of modem 40kbps, 52.6kbps, 128kbps and so on. Also speed will depend on peers who are seeding files to you.
Answer: You need to configure port forwarding , depending on the modem/ router the steps will vary. Find our what port your client is listening on then visit http://portforward.com/ for steps to configure the modem / router
Comment: Very useful link
Answer: Not exactly sysadmin related, but what the hey:
What a huge can of worms.
Many torrent clients (like Azureus) support UPnP so if your router also supports UPnP (and it is enabled), then the client can take care of it for you.
Other than that, you need to find out what port your software uses (it's usually a high port, like 16000 or something) and forward that port in your router to the downloading machine. Most software will allow you to choose your own port, so it shouldn't be too hard to find out what it is.
Answer: (I'm not sure that this question is in much relation to Sys Admin stuff)
Have you tried Google yet?
How to configure your router for bittorrent
and you should also configure your client correctly.


communities problem with union and find

Question: I am trying to solve the following problem:
Input is $2D$ array of integers, $M$, which corresponds to friendship relations. For example, if $M[1][2]=1$, $1$ and $2$ are friends (assuming symmetry it is also true that $M[2][1]=1$). If $M[2][3]=1$, then $\{1,2,3\}$ is a community. If all other entries are $0$, then $\{0\}$ is a community by itself, $\{4\}$ is a community by itself, etc. One can think of $M$ as representation of a graph with $V$ nodes, and $E$ edges. $M$ is $VxV$ matrix and the entries with value $1$ correspond to edges of an undirected graph. For the above example, the total number of communities is $V-2$.
I need to explain the following:
If we solve the above problem with union and find operations (weighted quick union), it will take $O(E+Vlog(V))$ time, explain.
I wrote the code for this. I am also including weighted union and find algorithm code as well below for completeness (but it is a standard known algorithm I guess). With the way I implement it, it does not look like this algorithm takes O(E+Vlog(V)) time. I need to understand how can this be done in O(E+Vlog(V)) time.
It is said that find operation takes O(log(V)) time because the tree is almost balanced with weighted quick union algorithm.
This is my code:

The code for weighted quick union and find (given):
<code>public class WeightedQuickUnion {

    int[] parent; // parent[i] = parent of i
    int[] size; // size[i] = number of sites in subtree rooted at i
    int count; // number of components

    /**
     * Initializes an empty union–find data structure
     * Each site is initially in its own
     * component.
     * n is the number of sites
     */
    public WeightedQuickUnion(int n) {
        count = n;
        parent = new int[n];
        size = new int[n];
        for (int i = 0; i < n; i++) {
            parent[i] = i;
            size[i] = 1;
        }
    }

    /**
     * Return the number of components.
     *
     */
    public int count() {
        return count;
    }

    /**
     * return the component identifier for the component containing p.
     * p the integer representing the item
     */
    public int find(int p) {
        validate(p);
        while (p != parent[p])
            p = parent[p];
        return p;
    }

    // validate that p is a valid index
    private void validate(int p) {
        int n = parent.length;
        if (p < 0 || p >= n) {
            throw new IllegalArgumentException("index " + p + " is not between 0 and " + (n - 1));
        }
    }

    /**
     * return true if the the item p and item q are in the same component.
     */
    public boolean connected(int p, int q) {
        return find(p) == find(q);
    }

    /**
     * Merge the component containing p with the
     * the component containing q.
     */
    public void union(int p, int q) {
        int rootP = find(p);
        int rootQ = find(q);

        if (rootP == rootQ) return;

        // make smaller root point to larger one
        if (size[rootP] < size[rootQ]) {
            parent[rootP] = rootQ;
            size[rootQ] += size[rootP];
        } else {
            parent[rootQ] = rootP;
            size[rootP] += size[rootQ];
        }
        count--;
    }
</code>
Comment: Do you have a question?  I'm not clear on what your question is.  Can you credit the original source of the question?  Debugging your code is outside of the scope of this site; we prefer concise pseudocode that doesn't require knowledge of any particular programming language.
Answer: You are using Adjacency matrix representation, instead just maintain a list of pairs of friend (i.e. edge list) and iterate it once.

communities problem with union and find


How can I tell whether or not a film has been broadcast on TV?

Question: Is there any way to determine whether or not a film has been broadcast on a TV station (particularly in the UK)?
Answer: For the UK:
The BUFVC has an archive of UK TV listings back to 2001. You need to be a member to access the full archive, but you can search the previous 2 weeks for free.
Alternatively, you can try The Guardian's TV Guide it's a bit hit and miss and it only tells you what channel the film was last broadcast on. For example it will tell me that The Shawshank Redemption was on ITV2, 12 Angry Men was on Sky movies crime & horror and that Rollerball was on TCM2.


Why are only the Normandy landings referred to as D-Day?

Question: Thinking about the anniversary of the Normandy landings, I was struck that the terms D-Day and H-hour were used to denote the start time of all allied military operations. Are there any specific reasons why the term has stuck to the particular operation of the Normandy landings?
Comment: @AmericanLuke That claim needs to be qualified as "*Western* European front" or "*amphibious* operation".  Else the Soviets would like a word with you.
Comment: Because it was DEE day.
Comment: It was the biggest operation of the war in the European front maybe...
Answer: The D merely stands for Day; in French, it's referred to as "Jour J". The term is indeed used for other D-Days, just not in regular English conversation.
Quoting from "D-Day" on Wikipedia:

The terms D-Day and H-Hour are used for the day and hour on which a combat attack or operation is to be initiated. They designate the day and hour of the operation when the day and hour have not yet been determined, or where secrecy is essential. For a given operation, the same D-Day and H-Hour apply for all units participating in it. When used in combination with numbers, and plus or minus signs, these terms indicate the point of time preceding or following a specific action. Thus, H−3 means 3 hours before H-Hour, and D+3 means 3 days after D-Day.

The article continues, to mention that several other lanugages use the initial letter in a similar fashion:

Hari H (Indonesian)
Час Ч (Chas Ch, Russian)
Dagen D (Swedish)
Dan D (Slovenian)
E eguna (Basque)
Jour J (French)
Lá L (Irish)
Tag X (German, an exception)
Ziua-Z (Romanian)

The article also links to "Military designation of days and hours", which has examples of other terms, just as F-Hour or O-Day.
Answer: The Normandy landings were referred to as D-Day in the U.K. and U.S. press because on the day of the landings, and in the following weeks, the code name for the operation (Operation Overlord) was still secret. The press wanted to report that 'the attack' on the Axis powers had started, and used the standard term D-Day as there were no restrictions on the use of this term. As it was used at the time in the press, the term has stuck. For example, the newspaper front page: http://www.archives.com/genealogy/newspapers-d-day.html has the headline "D-Day Chronology" near bottom.
Answer: It was the largest and most important in that war, so the general term attached itself to the specific day.
This kind of thing happens all the time, like all tissues being called Kleenex or all bleaches Chlorox.
Comment: What's Chlorox? I'll just get my Biro ...
Answer: D-Day was a watershed (though not necessarily decisive) event in World War II. It represented the counterinvasion of France, and a springboard for the a strike at the German heartland, thereby undoing Germany's "rise" in the 1940 Battle of France.
World War II is widely regarded as the greatest war in human history, not only compared to wars before, but to wars afterward. Certainly, everyone hopes that the scope and scale of World War II will never be exceeded.
In this context, D-Day means "THE Day" of THE greatest war in human history.
Comment: In the western point of view, anyway. In the grand scheme of things D-Day only ensured that the USSR would not dominate central Europe as well and ended the war maybe a year or 2 earlier. I find it abit odd that D-Day is commemorated but not Bagration, which occured 20 days later but netted about 3 times the casualties.
Comment: Three reasons: (a) Bagration, as large and important as it was, was one more step in a long,continuous war and not even the biggest battle in it; D-Day was a breaking point where a whole new phase of the War began, (b) we read the histories written in English which naturally focus more on the doings of their readers and the battles fought just a few hundred miles away, (c) and many of us had fathers or grandfathers who fought in France; much less so on the Russian Front.


False hrm results

Question: I use Garmin edge 520 with Garmin dual heart rate monitor and it shows completely false results like maximum hr >180 and average hr 150, while my ride is easy, slow and flat and I don't feel any discomfort. Measuring my hr with my finger I get much lower indications. Probably this happens because of an (controled) arrhythmia that I have. How to overcome the faulty results of my hrm? Is there any monitor or system that may be more acurate? Thank you in advance!
Comment: Do you know that these numbers are wrong? How do you take the reference measurement?
Comment: Ask your GP or heart specialist about the correlation of the readings and your condition. Fingertip readings and IR trans-skin devices are not the most reliable, especially vs. chest straps. (One thought, is your GPS software up to date?)
Comment: This is a common problem, and there are several possible causes.  Poor skin contact is one possibility, but this can also be due to a medical condition that makes the heart rate hard to read.
Comment: I never had much luck with chest strap models, especially out on a bike (as opposed to in the gym, mostly on a treadmill).  Some people find the LED-based upper arm ones better, but they tend to be more expensive.  I only borrowed one once briefly; it worked but that wasn't enough of a test to recommend either way
Comment: I had to try different HRM to find one that has reliable results for my physiology. (In that case a Sigma HRM). Others I tried measured either nothing or garbage.
Comment: If you really have a heart condition I guess a LED-based sensor (e.g. wrist watch) might work better for you. However they also require a good fit which might be hard on a bike with bent wrist and all the sharp shocks/hits.
Comment: Thank you for all the answers so far! I 'll check each one of them. Still waiting for more answers though!
Comment: Your very much not in the target market for these devices.  The devices are designed for a standard normal heart beat.  For someone not knowing they have a medical condition it can be argued that getting a high reading is better than a good reading.  It in a way alerts the user that there is some issue.  Maybe a device could be designed to target your condition but is that condition common enough and the signal regular enough to be able to re-work a device for it?
Answer:
Try replacing the battery, it could be running flat.
Make sure you're getting proper contact with your HRM to your chest - try adding some conductive gel.
Try a different soft strap, they wear out after a while.

I've had inconsistent readings from all 3 of the above issues at times.
Comment: Taking the battery out for 2 minutes, un-pairing the strap from your GPS and repeating the pairing procedure after having replaced the battery as your 4th possibility.
Answer: As mentioned already, one likely problem is poor contact.
One easy way to test for poor contact is to get the contact area wet - and I mean wet.
Put on your HRM strap and get your GPS unit.  Turn on the GPS unit, and when it's reading your HR - or when it should be reading your HR - take a full water bottle and soak in between the HRM strap and your skin.  Get it really wet.
Now see how your HR is reading.  If the reading improves and starts to reflect what you get if you measure your pulse by other methods, you have problems with your HRM because of bad contact.  You might have to wiggle your strap around a bit, or wet it more than once and wiggle it around a bit.
If this doesn't result in improved accuracy, it doesn't really mean anything - you could still have contact issues.
If you don't want to get your floor wet, do this outside or while standing in a shower or tub.
Comment: I never found tap water (or saliva) very effective, and often had to get a good sweat on to make reliable contact
Comment: Chemist's (drug-stores) sell conductive gels of the kind doctors use for ECG. You may also wet the patches on the strap with salt water.
Comment: The use of oil-based skincare lotions & creams may also be an obstacle to good conductivity. The instructions with my strap recommend soaping the strap every five uses to remove oily residues from the skin. A GP friend of mine told me once that there are people whose skin gives unreliable ECG readings.
Answer: Since no-one else mentioned it - this can be caused by the air causing some synthetic shirts/base layers to flap/flutter.
I had a top that got relegated to use on the indoor trainer because when wearing it outdoors my HRM would record 200+ any time I picked up any speed.
Comment: Interesting, I can confirm that this is a thing, at least with older generations of Garmin straps (the current HRM Pros don't show such anomaly). I wasn't fully sure if it is a flapping shirt interfering or the circumstance that an opened or thin jersey exposes the sensor to wind and drying up the sweaty/wet skin surface it depends on for reliable readings.
Answer: After trying the suggestions from other answers, consider that the numbers might be real. I do have the same problem and I returned my first HRM because I thought it was faulty. It turned out that I just do have unusually high heart rate without any known heart conditions, so that 150 is more or less normal for casual riding and the maximum is somewhere beyond 200. The "220-age" formula is not really true or even a good approximation.

False hrm results


Including pygame in google app engine

Question: I'm trying to include a PyGame library in my Google App Engine aplication:
<code>> import pygame
</code>
But I've got an import error:
<code>> from pygame.base import *
ImportError: No module named base
</code>
How can I import it?
Answer: You can't. GAE has a very restrictive set of libraries you can use. Here's a list:
https://developers.google.com/appengine/docs/python/tools/libraries27
Comment: Joe, that URL just lists the libraries that Google pre-installs on GAE for us to use as developers. You can certainly add third-party libraries, I add half a dozen or more on every GAE project I create, none of which are on that list. There are other restrictions (see my answer) such as linking to C libraries that they don't allow, which is the reason this doesn't work.
Answer: A bit of clarification: Joe's link is a list of 3rd party libraries that Google already has installed and available for you to use, but that's probably not why pygame doesn't work for you. For example, I use SendGrid and Flask in most of my App Engine projects and they works perfectly fine despite not being on that list (I just have to include them manually in every project I add)
As for pygame:
Libraries that rely on ctags or hook into other C libraries, are incompatible with how GAE does their thing. It's quite possible that some portion of pygame relies on third-party libraries (perhaps modules that load sound files that might use C libraries for playback). This will block pygame from being imported properly.
(update: Another post about a user having trouble running pygame on their Mac shows that pycame requires a library called pyobjc which very likely is not compatible with how GAE works, per my notes above)
I ran into this myself with a heavy math-related python package of which I only needed a small portion. It relies on a C library for maintaining precision with heavy variable typing. I ended up rewriting the small portions in pure Python using lots of int() and float() calls, and it worked perfectly.

Including pygame in google app engine


Audit app permissions easily in one place?

Question: Is there anyway to list all the applications installed on your phone and the permissions they require all on one page, or export the list so it can easily be audited?
Answer: Use market applications like Permission Watchdog or Permissions. Also, there are several others.
Comment: perhaps including comment into you answer would be simpler.
Comment: Unfortunately, Market application has a bug (or intended feature?) when not all permissions are listed when installing the application. This may a compatibility issue with software designed for older android releases... http://code.google.com/p/android/issues/detail?id=9365
Comment: @Nikolaenko, apparently it is on purpose and changed now:  http://android.stackexchange.com/questions/605/why-do-so-many-android-applications-require-permission-to-use-the-phone
Comment: @BlackShift, what do you mean by "changed now"? Changed by Android dev. team?
Comment: @Nikolaenko, I think I was unclear because it is unclear to me. I'm running cyanogenmod 6, android 2.2, and almost all apps ask for the permissions that your link claims are implicitely granted. So I don't know who changed this (cyanogen or android team).
Answer: Another app that I ended up using instead of Permissions is RL Permissions.  I prefer the interface.  As far as which one works better, I don't know.
Answer: aSpotCat is also a nice app for permission audit.
Answer: Permission Friendly Apps will list installed apps by their order of most demanding to least demanding permissions requirements. (It doesn't actually track or audit or adjust their behavior, though.)
Answer: Since no Android version is mentioned in the question, I'm proposing  a command-line based answer relevant to Android version 4.2.1 and above. This ideally is an OS-independent solution, OS on PC, that is.
Dependencies

Requires adb to be setup in PC.
Requires busybox binary. If the device is rooted, install Busybox app. Else, download busybox binary from official source, rename the binary to busybox, set Linux compatible executable permission on that binary for everyone and move it into device using
adb push LOCAL_FILE /data/local/tmp/   # LOCAL_FILE is the file path where busybox binary is located in PC

Requires aapt binary. If you're running a CM or its derivative ROM then ignore this requirement. Otherwise, for Android 4.x, you can consider downloading the binary from here, rename the binary to aapt, set Linux compatible executable permission on that binary for everyone and move it into device using
adb push LOCAL_FILE /data/local/tmp/   # LOCAL_FILE is the file path where busybox binary is located in PC .

For Android 5.x users, ask Google for assistance.

Here's my little script that does the magic:

#!/system/bin/sh

# Check if the busybox binary exists under /data/local/tmp/ or /system/xbin. Set the detected binary's path into the variable busybox or exit if file doesn't exist or executable permission not set
[[ -x /data/local/tmp/busybox ]] && busybox=/data/local/tmp/busybox || { [[ -x /system/xbin/busybox ]] && busybox=/system/xbin/busybox || { printf "busybox binary not found or executable permission not set. Exiting\n" && exit; }; }
# Check if the aapt binary exists under /data/local/tmp or /system/bin or /system/xbin. Set the detected binary's path into the variable aapt or exit if file doesn't exist or executable permission not set
[[ -x /data/local/tmp/aapt ]] && aapt=/data/local/tmp/aapt || { [[ -x /system/bin/aapt ]] && aapt=/system/bin/aapt || { [[ -x /system/xbin/aapt ]] && aapt=/system/xbin/aapt || { printf "aapt binary not found or executable permission not set. Exiting\n" && exit; }; }; }

# List package name of all the installed apps and save them in the file packages.txt under /sdcard
pm list packages | $busybox sed 's/^package://g' | $busybox sort -o /sdcard/packages.txt

# For each package name in the output we just saved, get the app's label using $path and $label, print a line and then finally list the permissions granted to the app
while read line; do
    path=$(pm path $line | $busybox sed 's/^package://g');
    label=$($aapt d badging $path  | $busybox grep 'application: label=' | $busybox cut -d "'" -f2);
    $busybox printf "Permissions for app $label having package name $line\n";
    dumpsys package $line | $busybox sed -e '1,/grantedPermissions:/d' -e '/^\s*$/,$d' | $busybox sort;
    $busybox printf "\n";
done < /sdcard/packages.txt

Demo output:

Permissions for app DisableService having package name cn.wq.disableservice
      android.permission.READ_EXTERNAL_STORAGE
      android.permission.WRITE_EXTERNAL_STORAGE

Permissions for app Indecent Xposure having package name co.vanir.indecentxposure
      android.permission.RECEIVE_BOOT_COMPLETED

Permissions for app Tags having package name com.android.apps.tag
      android.permission.CALL_PHONE
      android.permission.NFC
      android.permission.READ_CONTACTS
      android.permission.WAKE_LOCK
      android.permission.WRITE_SECURE_SETTINGS
...
...
Permissions for app Themes Provider having package name org.cyanogenmod.themes.provider
      android.permission.ACCESS_NOTIFICATIONS
      android.permission.ACCESS_THEME_MANAGER
      android.permission.INTERNET
      android.permission.READ_THEMES
      android.permission.WRITE_SECURE_SETTINGS
      android.permission.WRITE_SETTINGS
      android.permission.WRITE_THEMES

Save the script in PC into a file named perm_script.sh and move it into /sdcard using
adb push LOCAL_FILE /sdcard/   # LOCAL_FILE is the  path where you saved that file into PC

Run that file
adb shell sh /sdcard/perm_script.sh > OUTPUT_FILE   # OUTPUT_FILE is the path where you want to save the final output

The greater the apps installed in the system, the greater the time will be for the command to complete execution. In my device, it took around three minutes.
Related: Is there a native way to find all the installed apps that have access to a phone feature?


Which driver to be used for geforce

Question: I have  GEforce6150SE nForce430 graphic card. i m using proprietary tested driver.
I quited open source driver(used mare than 6 months) as last time it gave me  a problem (low graphic mode ) due to this i had to reinstall Ubuntu 12.10 . i had left with only that  option(solutions on net did not worked)
so which driver is saver to use (i don't want to get that problem again )
Answer: The proprietary driver from Additional Drivers (search for Additional Drivers in the Dash and click on the Additional Drivers icon to open Additional Drivers) should give you better performance than the open source driver. Select the Nvidia driver from Additional Drivers that has [Recommended] appearing after it. The recommended GPU driver is from the Ubuntu Software Center, and is supposed to be safe and run properly, and be safer than any other graphics driver that you might download from a manufacturer's website.
It happens occasionally for certain models of graphics processors, especially the newest models of graphics cards on older versions of Ubuntu, that the proprietary graphics processor driver will cause Ubuntu to boot to a black screen with a low-graphics mode message box. If this problem can't be solved in any other way, then you may have to use the open source graphics driver instead of the proprietary graphics driver.
Answer: install "synaptic".
synaptic menu: settings/repositories/additional_drivers
choose: "using .... nvidia-319 (proprietary,tested)"
click button: "apply changes"
on synaptic mainscreen, click button: "mark all upgrades"
click button: "apply"
reboot your PC.
the above is the surest, quickest, safest way to get the nvidia driver installed and working.
to access the nvidia gui, click on the dash and search for nvidia.

Which driver to be used for geforce


How do you dodge Sivir's boomerang ability?

Question: Whenever I lane bot against a Sivir, she hits me every single time with her boomerang, making me have to go back to the base a lot. The people on my team always tell me to just dodge her ability, but how do you do this? Does it just come with practice, or is there an easy way to predict where and when that boomerang is gonna fly at you?
Comment: Do you mean the large Skillshot boomerang or the individual riccochet bounces?
Comment: The large boomerang skillshot (q)
Answer: Sivir's Boomerang Blade can be an annoying harass, both at early level and late game. Unfortunately, it mostly takes practice to be able to avoid it. But there are a couple of tips that I think (hope) will be helpful in the long run.
Placement
Sivir's Boomerang Blade has a fairly large attack radius. Where you are in relation to where Sivir is when she launches the attack can make a fairly significant difference. The important thing to remember, though, is the further you are from her, the longer you have to react. Try to remain at a distance as much as possible when facing Sivir; especially in early game. One more important point on placement, the more minions between you and Sivir, the less damage you will receive if Boomerang Blade hits you. Each enemy it hits makes the damage to the next enemy lessen.
Movement
Unfortunately for you, sometimes dodging her initial attack ins't always enough. Her blade will track with her, if she moves up or down on the battlefield. You should always move in the opposite direction from Sivir. In the following image, consider your Champion to be X, while the colored arrows show the path of the blade upon return, in relation to Sivir's movement.

One last point worth mentioning is this:  While the camera is zoomed in in that image, it's important to remember the high range of Boomerang Blade. It will extend to the far edge of the screenshot.
If you can't always avoid the first shot, pay close attention to avoiding the return strike. But in the end, it really comes down to practice, practice, practice.
Answer: Strafe!
While it may sound like a simple answer, remember that Boomerang Blade is aptly named and will hit you on its return. Often, when enemy champs fire a projectile, your instinct is to head straight backwards to try to get out of range.
Unfortunately, with Boomerang Blade, it means you're just lining yourself up to get hit a second time. Try to learn how close you can safely get without getting hit, though this can be difficult given its long range.
If you can't dodge that first hit, after you've been hit by it once, try moving perpendicular to the path that Boomerang Blade was thrown in. This will at least give you a better chance of getting out of the way of its return, though skilled Sivir players will take advantage of the fact that they can alter Boomerang Blade's return path by moving, potentially leading the Blade back to you regardless. Keep that fact in mind and watch where Sivir moves to try to get a handle on which path the Blade will take heading back to her.
In addition, increasing your movespeed via early boots can also help get you out of the path quicker. If you know you're laning against a Sivir (or other champ with a long poke), try to prioritize your item purchases in order to get boots as soon as possible, especially if you're playing a champ with very low base movement speed. Earlier boots mean you can dodge more effectively, which means you can lane longer without having to go back for healing and buying health potions.
Comment: Thanks for the advice. I do try to move sideways when I get hit with the boomerang, but it seems that I'm always not fast enough to get out of the way in time, guess I'll just have to keep practicing it.
Answer: Try to stay back as far as possible while still keeping up your last hits and the occassional harrassment.
One tip that always works well with opponents who use skillshots is to start with a pair of boots or, if you cant start with them, get them as soon as possible. The extra movement speed is definitely noticeable against these sort of champions.
Answer: Start with boots if you can and either stay back to avoid it all together, or move side to side instead of back and worth to dodge it. it all comes down to his predictive skills and your reflexes.
Answer: Strafing is the best way to dodge the boomerang ability. The lesson of strafing is important to dodge any skillshots and will come in handy in all situations either going 1v1 against another champion or in a team fight.
Answer: Try to keep some minions between you and Sivir. Since every target after the first takes 20% less damage from Boomerang Blade, a good Sivir player will only use it when the only thing in its flight path is you.
By using your own minions as shields, you will either reduce the amount of damage you take or discourage your opponent from using Boomerang Blade at all.
Answer: :) Boots+3 pots to start, always great vs. skillshot champs. It keys off of AD as well, so go Ninja Tabi (Or something else with armor, like Wriggle's) if she's hitting that hard.
Comment: Probably not the best idea to build wriggle's or ninja tabi's on an adc.
Answer: Try to expect the unexpected as we say. You can always stay a bit far and dodge when you see her shooting the boomerang. Also you can keep moving a lot in the lane.
Answer: In a more general sense, knowing the abilities of the champions you are facing against helps you in a matchup.  For example, similar to Sivir, if you are against a Caitlyn, choosing to strafe up and down will make it harder for you to get hit by her Piltover Peacemaker.  On the other hand, if you are against an Ashe, strafing up and down won't help as her Volley is a spread attack, so running away from Ashe is better to dodge that ability.