SDP and chromatic number upper bounds

Question: Are there any references for finding non-trivial upper bounds to chromatic number using semidefinite programming?
Comment: "outer bounds" ? also, are you referring to the Lovasz theta function ?
Comment: @Suresh: Here by outer bound, I imply upper bound and by inner bound, I imply lower bound. I thought Lovasz theta is only for outer bounding the independence number? Would it apply to chromatic number as well? Since chromatic number is implicitly a minimal number under some constraints, I am curious if there are any Lovasz type outer bounds to chromatic number and Lovasz type inner bounds for independence number as well?
Comment: You might want to edit to use the more standard terminology ? (at least standard in algorithms)
Comment: @SureshVenkat done
Answer: SDPs usually provide relaxations, so for a minimization problem you'll get a lower bound. The Lovasz theta function does provide such a lower bound on chromatic number (see wiki). Upper bounds can be provided by rounding schemes (constructive or otherwise). In general, if you have an upper bound $U$ on the integrality gap of the SDP, you can scale the objective of the SDP by $U$ and you'll get an upper bound as well. However, there exist graphs for which the Lovasz theta gives a lowerbound of $k = O(1)$ and the chromatic number is at least $n^{1 - 2/k}$. There is some hope that higher levels of the Lasserre hierarchy can give stronger relaxations. However, notice that chromatic number is  hard to approximate within $n^{1 - \epsilon}$ (see this) in general (i.e. if you're not just interested in the promise problem where the yes instance has constant chromatic number). So, for any SDP, integrality gaps better than $n^{1-\epsilon}$ will either be restricted to cases where the SDP relaxation has  constant value or will be nonconstructive (i.e. superpolynomial time rounding or superpolynomial size relaxation), unless P=NP.
Comment: in the Laserre hierarchies paper (http://www.cs.princeton.edu/~rongge/LasserreColoring.pdf) there are some references for integrality gap results: look at references 14, and 15. Also Mario Szegedy showed the Lovasz theta has integrality gap $n^{1-\epsilon}$ w.r.t. independence number if and only if it has integrality gap $n^{1-\epsilon}$ w.r.t. the chromatic number (http://www.cs.rutgers.edu/~szegedy/PUBLICATIONS/theta.ps). Alon and Kahale show an integrality gap of $n^{1-\epsilon}$ for any $\epsilon$ for Lovasz theta w.r.t. independent set. I am not an expert, follow refs in these papers.
Comment: very good answer. almost what I am looking for. The notion of integrality gap between the lower bound for chromatic number as provided by SDP and the correct chromatic number is new to me. Is there a reference that provides more details on the study of the integrality gap? Moreover the graphs I am looking at are product graphs. Are there any work on integrality gap for sdps in relation to the chrmatic number?
Comment: about product graphs: the Lovasz theta behaves very nicely with tensor products of graphs. this might be a way to amplify gaps, but i don't know much about the existing integrality gap constructions and i am not sure if they work this way.

SDP and chromatic number upper bounds


To kill harmful animals

Question: Considering that kill can bring bad karma, what must be done with some harmful animals like aedes aegypti, triatoma infestans, ticks etc., when it is on our way? And if they can be killed it means we can tranquilly kill a homo sapiens that is effectively more harmful than those creatures?
(This question does not concern legal issues, just karmic e religious issues.)
Comment: You need to understand that the harmful animals are also here for a purpose.It is our duty to avoid them as much as possible but it is not in our rights to kill them.
Comment: Interesting way of thinking. Karma is highly complicated. There is nobody on this earth who has deciphered karma (unless they are self realized or God). Karma is not associated with Good or Bad. That is our own delusion. Karma simply means 'Whatever you do, comes back to you!'. If you kill a human being with bad intentions, then chances are (unless you attain self realization) it will come back to you. If you killed the human being with good intentions, then too somebody else may do the same to you (unless you're self realized) ! Thus Lord Jesus said 'Treat your neighbor as yourself!' All best
Comment: @Sai, "avoiding good vs bad" is correct guideline; I too think the same. This is 1 of the very few places where Veda & Gita fall apart. The usual childhood teaching in a typical household is based on Veda, which advises to do good & leave bad. It's helpful for society/culture building. But Gita is more self centered, hence it was advised in private when the preacher was feeling Oneness with asker. Like advising self! Karma for which we can no more answer "Why I do?" seems *NishkAm* to me for now, as it's most natural. This is why Karma of creating universe doesn't bind God. More thinking reqd.
Comment: @Sai I think that as first you must cherish, protect and respect the life within you. I belive that we are living in this material life because we have to learn all this things. And if tiger will attack, you must first protect what has been given from the gods: the life itself (God seed). But if tiger will kill you, you must forgive him because every one is living with their own level of awarenes. All the best!
Comment: However if you killed with a genuine desire to defend yourself (lets say a man is coming after you with a knife), then I am not sure what would happen, because in such cases you are reacting, rather than 'acting'! For example, if you killed a tiger, because it is trying to eat you. You are simply 'reacting'. You are not acting. It is incredibly impossible to understand karma to a 100% accuracy. Thus the sadhakas get a general understanding of karma (do unto other as you would have done unto you) and move on to the goal of Self Realization, thereby karma is completely obliterated. :)!
Comment: @iammilind I admire your reverence for the Gita. :) You said it right that in Gita Lord Krishna says that the work that is done for the sake of work (without desire for the fruit) is non-binding (paraphrased). This same truth has been spoken of by different seers in different ways. Sri Ramakrishna, said in His Gospel that 'The real essence of the Gita is what you get by reversing the word Gita into Tagi (or Tyagi some language), aka renunciation. Renounce your desires, i.e. desire for fruits and attain God!'. Very good.
Comment: @urosjarc You are absolutely right. Thanks :) !
Answer: My previous answer was entirely based on my own understanding and without any Scriptures to support it.
Now,here is a completely revised answer that is based on Scriptures:

When one's life is in danger, he can kill a Brahmana, Vysya, Kshatriya or a Shoodra or even a cow, horse or any other animal, to
  protect his life from them. This will not earn him any sin. ...The
  king, for the sake of the gods and the Brahmanas, should kill harmful
  animals such as the lion, tiger etc. In times of distress, the king
  may kill and eat an animal, that is fit to be consumed. He should
  never indulge in this act, in any other circumstance, except for the
  sake of gods and Brahmanas.

The above passage is from Brahmanda Purana,Uttara Khanda.
The words are those of Brihaspati(Deva Guru) and the conversation is between him and Deva Raja Indra.
According to Vishnu Smriti:

Protecting (one attacked by robbers, or by tigers, or otherwise in
  danger) is more meritorious than any (other) gift.
By doing so he obtains that place of abode (after death) which he
  desires himself.
188. He who kills (in his own defence a tiger or other) animal with sharp nails and claws, or a (goat or other) horned animal (excepting
  cows), or a (boar or other) animal with sharp teeth, or an assassin,
  or an elephant, or a horse, or any other (ferocious animal by whom he
  has been attacked), commits no crime.(Chapter V)

So,it seems,killing a potentially dangerous animal is not a sin provided you are being attacked by it.
Comment: Ahimsa is not always Param Dharma. Dharma is highly relative and subjective, but truth is one. A Kshatria's duty is to kill enemies on battlefield and save his people. Similarly soldiers must kill and they die on battlefield. That's the reason all those who die on battle field go to heaven. And i'm not the one who down voted your answer.
Comment: @AnilKumar I agree that soldiers who die fighting for their country goes immediately to heaven but what about those who emerged out victorious and alive after war?Anything mentioned about them in scriptures?An act of ahimsa is always followed by another act of the same nature as a consequence.This is what i have understood.
Comment: Rama, Krishna and even Vishnu and Shiva killed many evil demons.  Pandavas wanted to visit Kailas (Shiva) to clean sins. So, Dharma is highly relative and changes with Yuga too. You can't be a good King or leader or politician by following Ahimsa always in Kali Yuga. A Sanyasi should never resort to violence. So, it actually depends on situation and your profession..
Comment: So,the duties of a ksatriya will naturally involve such acts  that creates more bad karmas than those of a Brahmin.So,what i feel is any act of himsa is bad as that one act creates an infinite chain of such acts.But of course to imagine a world completely free of any kind of himsa is un realistic.
Comment: You are only considering act of killing but he is actually gathering a good karma too by saving his people. If a mosquito though it didn't bite you, you can kill it as it will definitely cause you a disease when it bites you. So, you are thus saving your family members. Actually you are acquiring good karma too here. Case would be here self defense and Karma may be zero. "Swadharma is more important than Paradharma", so your self defense is your foremost Dharma.  As i said this Dharma is highly relative when we live in Maya.
Comment: Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/35995/discussion-between-anil-kumar-and-rickross).

To kill harmful animals


Caad10/12 sizing

Question: I'm looking to buy a used CAAD 10 or 12 but since they are quite far away, I can't test ride them so I'll have to guess the correct size. I am 173cm tall and an inseam of barely 80cm without shoes. I did test a 52cm CAAD 12 a few years ago from my friend and since I mostly ride hardtails, I felt kinda cramped, maybe I'm just not used to. Any advice?
Comment: Do you have access to anything to test-ride ?  Comparing the various measurements might give you some ideas, but at best this is going to be a crapshoot for you.   Comfort and fit is such a personal thing that noone can tell you what will be best for you.  Perhaps you should forgo the distant options and search out something closer that you can test out.  Otherwise its a gamble, though you can always resell it if the fit is wrong.
Comment: @Criggie: "Comfort and fit is such a personal thing that noone can tell you what will be best for you." Bike fitters are going to disagree ;)
Comment: @Michael true, but that's a back-and-forth discussion between fitter and fittee which customises the result.  DanK's answer **suggests** that 54cm is the right frame size, but really its only a starting point.  Otherwise a bike fitter's whole job could be reduced to that one table. Obvs there's a lot more to it than This Height/Inseam == This Framesize.
Answer:
If you felt cramped on a 52cm then maybe a 54cm would be the better option.
You can always make minor adjustments to the stem and seat to get a better fit.
Unfortunately only you are going to know what one is better.
I'm about a cm taller than you but ride a 56cm but my bike is a Cube and their measurements are different to Cannondale so as you can see with each bike manufacturer you may need a different size frame.
I have added the Cannondale size guide for reference.
Comment: I'd still tend to pick the smaller frame. You can go from a 90mm stem all the way to 140mm (that's like two "sizes" more reach) if it's too small and you can raise the saddle a lot as well.
Comment: For me, that table suggests a 63cm frame is too short for my legs, but a 60 cm frame is right for my height.   Tables are only a starting point.   I ride a 57cm cannondale frame, but with a lot of seat post and a relatively short stem.
Comment: But officially, even if the 52cm felt cramped, what should I aim for? 52 or 54?
Comment: @Rgth122twwt: How long was the stem on the 52cm frame? How did it look to an observer? If you come from a too large frame a good fit might actually feel cramped.

Caad10/12 sizing


Issue with Full Screen in Zoom Call

Question: I am not sure if this happens with other applications, but I have seen it happen in Zoom. Whenever I am in a call and go into a full screen view, the application goes into full screen mode, but only takes up like 1/4 of the top left of the screen and becomes unresponsive until I move it to a different workspace, where it is no longer in full screen mode.
Answer: I believe it is a zoom bug not elementary issue, it happens to all my devices using linux in general and teams or skype does not make the same issue, just enter full screen from elementary itself not from zoom (search shortcuts for full screen).

Issue with Full Screen in Zoom Call


How to split app screen on my Mac?

Question: I can reduce the size of pages to make multiple of them fit on my screen, but then they are never oriented properly :( Is there a way to actually split my screen as a command on my MacBook Air? I imagine that would line the pages up automatically.
Comment: Welcome to Ask Different, Lacy. I've added the tag window manager since many operating systems add these to handle arrangement of windows. If you search for popular questions in that tag, it might get you bountiful suggestions on how to manage windows on macOS.
Answer: The supported Apple way of using split-screen for El Capitan onwards is documented at https://support.apple.com/en-gb/HT204948 in the section titled 'Use two apps in Split View'. It works nicely for apps that support it. The most up-to-date docs for Mojave are at https://support.apple.com/en-gb/guide/mac-help/use-apps-in-split-view-mchl4fbe2921/mac
You can hold and drag the green maximise button of a window to one side of the screen to 'lock' it in position, then select another window to fill the other side. The same functionality is also available in Mission Control (ctrl-up arrow).
I'm not aware of a command that will do what you require, but it's possible using the GUI gestures.
Comment: The app BetterTouchTool can actually automate the long-click + drag motion, and you can assign this action to a macro. In BTT the action is called `Open Native OS X Split View for Window`, and supports both left and right sides of the screen. Choosing the app for the other half of the screen requires using the mouse, however.
Answer: While as mentioned in the other answer, Split View feature available in OS X El Capitan and later lets you use two apps side-by-side.
However, that approach comes with certain limitations. The apps need to be in full-screen mode, there can be only two apps side-by-side, and both of them share half of the screen each.
You can use a 3rd party app that lets you quickly and easily align app windows. Divvy is one such (paid with free trial) app that lets you easily manage app windows. It lets you configure a keyboard shortcut which gives you control to quickly and precisely set frontmost app window layout.

Divvy is available for download on the Mac App Store:

Divvy - Window Manager

Free trial can be downloaded from the app homepage:

Mizage - Divvy

Note: No affiliation whatsoever with the developer of the app. I find the app useful in my workflow and use it on a regular basis.
Comment: Divvy is the one I recommend or get for people that want serious automation in their window management. Getting started with [side by side arrangement tools is nice](https://apple.stackexchange.com/questions/50330/) and the [massive list](https://apple.stackexchange.com/questions/9659/) has some other gems in it.
Comment: All good suggestions, I use [Magnet](https://magnet.crowdcafe.com) myself. I refrained from listing 3rd party tools in my original answer to avoid complicating it, and without assuming the OP's needs beyond the basics.

How to split app screen on my Mac?


how to use tikz plot coordinate axes and arrows?

Question:
A planner figure, any visual tools can help?
Comment: Well, general relativity is even harder for beginners, but this does not mean that others will do *your* computations for you. Likewise, if you have difficulties with drawing *your* picture, this does not mean that others take over. For newcomers we sometimes make exceptions, but after the first answer you have already an idea what an MWE is. So please show us what you've tried.
Comment: @marmot i will try after class, thank you. if anyone have answer,  comment after i have tried.
Comment: Next time please don't upload images that are not upright. Seeing those is much harder than doing others.
Comment: @ArtificialStupidity i see, it's not upright, I will correct. thank you!
Answer: considering your answer as starting point (as missing mwe in your question)...
with use of tikz librariesangles (for drawing angles), \arrows.meta (for nice arrows), calc (for drawing orthogonal vectors) and quotes (for angle labels), and use polar coordinates the code for your image can be as follows:
\documentclass[tikz, margin=3mm]{standalone}
\usetikzlibrary{angles, arrows.meta, calc, quotes}

\begin{document}
    \begin{tikzpicture}[% styles used in image code
         > = Straight Barb, % defined in "arrows.meta
dot/.style = {circle, fill,
              minimum size=2mm, inner sep=0pt, outer sep=0pt,
              node contents={}},
box/.style = {draw, thin, minimum  width=2mm, minimum height=4mm,
              inner sep=0pt, outer sep=0pt,
              node contents={}, sloped},
my angle/.style args = {#1/#2}{draw,->,
                               angle radius=#1,
                               angle eccentricity=#2,
                               } % angle label position!
                        ]
% coordinate axis
\draw[->] (-3,0) -- (6,0) node[below left] {$x$};
\draw[->] ( 0,0) coordinate[label=below:$O$] (O)
                 -- (0,6) node[below left] {$y$};
% axis units
\draw[->,thick] (0,0) -- (1,0) node[below] {$i$};
\draw[->,thick] (0,0) -- (0,1) node[right] {$j$};
% dashed line
\draw[dashed]  (-2,0) coordinate (s)
                      -- ++ (32:4.2) node (d1) [dot];
% angle theta, used "angles" and "quotes" library
\pic [draw, my angle=12mm/0.8, "$\Theta$"] {angle = O--s--d1};
% solid line
\draw[thick]    (d1)  -- node (m) [box] ++ (32:3) node (d2) [dot];
% angle N_z
\pic [draw, my angle=6mm/1.5, "$Nz$"] {angle = d2--m--d1};
% forces in y and x direction
\draw[->] (m.center) -- ++ (1,0) node[below] {$ F_xi $};
\draw[->] (m.center) -- ++ (0,2) node[left] {$ F_xj $};
% vectors v_1, v, v_2, used "calc" library
\draw[->] (d1) -- ($(d1)!12mm! 90:(d2)$);
\draw[->] (d1) -- ($(d1)!12mm!270:(d2)$) coordinate[label=below right:$v_1$] (v1);
\draw[->] (m.center) -- ($(m.center)!12mm!270:(d2)$) coordinate[label=below right:$v$] (v);
\draw[->] (d2) -- ($(d2)!12mm!270:(d1)$);
\draw[->] (d2) -- ($(d2)!12mm! 90:(d1)$) coordinate[label=below right:$v_2$] (v2);
% dashed line between vectors v_1, v_2
\draw [dashed] (v1)--(v2);
    \end{tikzpicture}
\end{document}

Comment: In the image attached to the question, `v1`, `v` and `v2` are not of the same length.
Answer: Yeah, it is not difficult. when you meet problems, do not afraid, just do it step by step.
Although my method based on translation and rotation,\draw everything, not smart, the code is very redundant.
There is the first version. I will keep learning. next, I will use \coordinate to make code simple and efficient.
code as follows:
\documentclass[letter]{article}
\usepackage{tikz}
\begin{document}
\centering
\begin{tikzpicture}
\draw[->] (-2.4,0)--(5,0) node[below] {$ x $}; %coordinate
\draw[->] (0,0)--(0,6) node[left] {$ y $};

\draw[->,thick] (0,0)--(1,0) node[near start,below] {$ O $} node[below] {$ i $}; %unit coordinate
\draw[->,thick] (0,0)--(0,1) node[left] {$ j $};

\draw [dashed,xshift=-2cm,rotate=32]  (0,0)--(4.2,0); %line
\draw [xshift=-2cm,rotate=32]  (4.2,0)--(7.2,0);
\draw[->] (-0.8cm,0) arc (0:32:1.2cm) node[left=1.2pt,below=2.1pt] {$ \Theta $}; %arc 1

\filldraw[fill=black,xshift=-2cm,rotate=32] (4.2,0) circle (0.1cm); % M1
\draw[->,xshift=-2cm,rotate=32] (4.2,0)--(4.2,1.1);
\draw[->,xshift=-2cm,rotate=32] (4.2,0)--(4.2,-1.45) node[name=v1,right=1pt,below=1pt] {$v_1$};

%rectangle (5.7)
\draw [xshift=-2cm,rotate=32] (5.6,-0.2) rectangle (5.8,0.2);
\draw[->,xshift=-2cm,rotate=32] (6.0cm,0) arc (0:180:0.3cm) node[left=3pt,above=10pt] {$N_z$}; %arc 2
\draw[->,xshift=-2cm,rotate=32] (5.7,0)--(5.7,-1.4) node[right=1pt,below=1pt] {$v$}; %v

\filldraw[fill=black,xshift=-2cm,rotate=32] (7.2,0) circle (0.1cm); % M2
\draw[->,xshift=-2cm,rotate=32] (7.2,0)--(7.2,1);
\draw[->,xshift=-2cm,rotate=32] (7.2,0)--(7.2,-1.3) node[name =v2,right=1pt,below=1pt] {$v_2$};

\draw[->,xshift=-2cm,rotate=32] (5.7,0)--(5.7,0) node[name =c1] {$ $};
\draw[->,xshift=-2cm,rotate=32,rotate around={-32:(c1)}] (5.7,0)--(6.7,0) node[below] {$ F_xi $};
\draw[->,xshift=-2cm,rotate=32,rotate around={-32:(c1)}] (5.7,0)--(5.7,2) node[left] {$ F_xj $};
\draw [dashed,xshift=-2cm,rotate=32] (4.2,-1.45)--(7.2,-1.3);
\end{tikzpicture}
\end{document}

Reference: http://texdoc.net: pgf manual.
Comment: Please don't link to that manual, version 3 of TikZ is around five years old already. Link to CTAN (or texdoc.net) instead.
Comment: (i) please, always provide complete small document, not only code fragment (ii) with your code (after adding extend it to mwe) i can't reproduce image showed in your answer.
Comment: i saw your corrections :-). now works. well, meantime i write my suggestion how to draw your image. see if it can be helpful :-)
Comment: @Zarko already improved, thank you, let me know if you have any questions about it.
Comment: @Zarko thank you, it is very helpful :-). I spent much time drawing orthogonal vectors $F_xi$. your answer is simple than me, especially in readability of the code. I have an irrelevant question, how do you think about the `Asymptote`, I saw the document in the official site,  is it more convenient in drawing 3d graphics?
Comment: i never not use asymptote, not see its official site. from some questions/answers here i can conclude that it is quite powerful tool.
Comment: Yes, the great advantage of asymptote 3d is that you can rotate objects with a few pdf readers, for example, here I wrote a die that you can rotate on itself with the mouse: https://tex.stackexchange.com/q/379969/138900

how to use tikz plot coordinate axes and arrows？


Post-processing to remove background reflections on bald heads

Question: I've done a series of chroma key shots of some co-workers for our website and generally everything came out great, except one of our guys is bald and, well, the green is reflecting onto his head. So, the question is, does anyone know of a good way to remove this sort of highlight in post-processing? I'm using Photoshop CS5.
Comment: It's funny, but the bigger laugh was all of us thought his photo would be the easiest, it took far and away the most work!
Answer: There's probably several different ways to skin this cat (there always are in Photoshop), and it's be easier to give specific input if there was a picture to look at, but in general I'd probably tackle the problem with something like this:

Create a Hue/Saturation Adjustment layer
Modify the layer mask such that only the area with bleed problems is selected
Pull saturation out of the green out slowly using mostly the 'Greens' channel (Alt+5) and a bit in the Master channel (Alt+2).

As a 'future reference' thing, keeping subjects at least 6 feet from the backdrop will help keep bleed to a minimum.
Comment: 4. make them wear wigs (feel free to downvote me, but i had to say this :D)
Comment: +1 and accepted, it's what I ended up actually figuring out for myself in the end!
Comment: @John: Great minds, and all that... ;-)
Comment: Maybe next time a polarizing filter could help to reduce the reflection.
Comment: + 1 for the note on keeping subjects to at least 6 feet from backdrop.
Answer: I also am a make up artist and I say put a little face powder on his head to remove that shine.


How to treat illogical survey responses

Question: I have submitted a survey to a sample of artists. One of the question was to indicate the percentage of income derived by: artistic activity, government support, private pension, activities not related with arts. About 65% of the individuals have replied such that the sum of the percentage is 100. The others don't: for example, there are who answers that 70% of their income derived by his/her artistic activities and 60% by income government, and so on.
My question is: how should I treat these observations? Should I delete, modify or keep them?
Thank you!
Comment: In your example, is it possible they sold art to the government, and interpreted that as money coming from two sources, thus counting it in two columns? It may be the case that they interpreted your survey differently than you did when you made it. It's also quite probable that they are somewhat mathematically illiterate. Neither of these cases make their results unusable, just possibly difficult to resolve. For the record, worded as you did here, I'd have the same interpretation as you.
Comment: @LioElbammalf Large sample size doesn't cancel out the issues caused by non-random exclusion criteria such as "respondent can't do math properly"
Comment: Is this even necessarily inconsistent?  Isn't it possible that those categories are not mutually exclusive?  E.g., the respondent earns 30% of his income from artistic work *paid for by the government*.
Comment: @Ben, absolutely. What is way more important than dealing with the issue is to design the questionnaire in such a way that it is unambiguous about this.
Comment: As long as you mention what you've done you can do anything and your work will be published with these caveats. However you haven't told us how many people you've got - getting rid of 35% of your sample is less of a concern if you've thousands of responders than if it is 35% of 40 - the problem arises when you're dipping into it being a stretch to make statistical analysis. So - **sample size?**
Comment: This is a shining example of why one should ALWAYS test surveys before running them on the full sample. Given a 35% rate of unexpected results, even a small test would almost certainly have revealed this issue and probably given some insights into how it should be addressed.
Comment: It's common to have percentages not adding up to 100%. https://en.wikipedia.org/wiki/Ninety-ninety_rule  In your case it's probably like "uh, this is like 60% of my income, I guess. and that one? a bit more actually."
Comment: Is this intended to be an actual measure of income streams or a perception of them?
Comment: You're right...the total sample is 1100 individuals
Comment: I've changed your question heading slightly.  Please roll back the edit if you don't think it fits.
Comment: This is more a UI/UX tangent, but if you provided the survey to them in electronic (i.e. web page) format, you could include some simple scripting that shows a red box at the top or bottom of the percentage fields saying "total from all sources must equal 100%"; each time they change a field, recalculate, and if they have it right, dismiss the box.
Comment: @Acccumulation Of course it doesn't but I only said it was less of a concern. Comments are intended to ask for more information, not provide all the answers.
Answer: This is a good situation for a sensitivity analysis.  Analyze your data in each of three ways --

As they are
After excluding "the illogicals", i.e., people whose percentages don't add up to 100 (or 100 +/- 10)
After adjusting where necessary so that each person's percentages add up to 100

Then compare results, sharing any rationale you can develop as to which results might be more accurate, or more accurate in certain respects.
You can also investigate the range of ways in which the logicals and illogicals differ, if any.  Do the illogicals tend to report higher incomes?   To show greater support for certain ideas or programs?  To skip more questions?  To evince more bias in the sense of straightlining or disproportionately choosing middle responses or extreme responses?
With about 400 or these illogicals, you have enough data even to assess the relationship between degree of illogicality and degree of a given type of bias.  Something like a dose-response relationship.
What you learn from these investigations might be fed back into your plan for dealing with the illogicals when it comes to the main analyses of interest.
Answer: As already alluded to here, those answers aren't necessarily illogical.  For example, you say

The others don't: for example, there are who answers that 70% of their income derived by his/her artistic activities and 60% by income government, and so on.

That makes perfect sense if 30% of income is derived from artistic activities done for the government.  Then we really have three groups:

Artistic activity, unrelated to government:  40%.
Government, unrelated to artistic activity:  30%.
Artistic activity subsidized by government:  30%.

Those numbers add up to 100%.
Consider the following questions:

Are food stamps government or activities not related to the arts?
Is Social Security government or a pension?
Is a government pension (former government employee) a private pension or government?
Is a government grant to paint a painting artistic activity or government?
Is a job teaching arts at a local school government or artistic activity or activities not related to the arts?
If retired from a job in the arts (teaching or commercial, e.g. drawing gift cards), is the pension private or artistic activity?  Or in the case of teaching, possibly government?

You seem to want these categories to be mutually exclusive.  However, I don't think everyone would interpret them that way.  You may have clear thoughts on how those activities should be categorized, but it's not clear that your respondents had the same divisions in mind when they answered.  At minimum, if you want the numbers to add to 100%, you should tell people that.
Personally, I think that the best approach to this kind of a problem is to do a kind of focus group.  In a traditional survey, you may not be able to validate answers.  So call or visit people who would be targeted by the survey and start a conversation.  Then when they give answers that you don't understand, ask them why.  And beyond that, ask them how you should have asked the question so that you'd get the kind of results that you want.  This works more like a focus group in that it is interactive.
Once you've done that, then you can get a better idea of how to handle the responses that don't fit into your format.  For example, you might take the 30% extra and subtract half from each.  Then you'd have 55% artistic activity and 45% government.  Or you might recategorize as 40% private artistic activity, 30% government-sponsored artistic activity, and 30% other (in this case, government support unrelated to artistic activity, e.g. food stamps or rent support).  Or throw out the survey and redo it, because people are not understanding your categories properly.  Part of this depends on what you understood the categories to mean as well as how they interpreted it.
Too late now, but for future surveys, consider doing a regular focus group before the survey.  Then you can test your questions in the group environment and improve them.  You may even find that you get additional questions from the group.  If it's too difficult to do this in person, consider doing it online.  Or do a test survey (of a smaller number of people, validating responses with follow-up questions) by phone personally before doing the real survey.  Any of these can help you make your questions clearer.
For example, perhaps your real categories should have been private income from artistic activity; government-sponsored artistic activity; private pension from a former job; other income unrelated to artistic activity.  Or something different.  Part of the problem is that I can't tell what you want, which makes me think your respondents couldn't either.  If there are three different interpretations, it's almost like you are mixing responses from three different surveys.
Answer: I cannot give you an answer for the general case of illogical responses. But for this specific type of question - been there, done that. Not only in a survey, but also in semistructured interviews, where I had a chance to observe how people come up with this kind of answer. Based on this, as well as some general experience in observing and analyzing cognitive processess, I would suggest: normalize your data back to a sum of 100%. The reason is that people seem to first go to the most salient category - in your case, that would be the largest income - give a gut-feeling estimate for it in percent, then start thinking of the next smaller categories and base their estimate relative to the anchor of the first category, plus that of further already mentioned categories.
For an example, a train of thought will go like: "My first source of income is certainly more than half. It makes what, 60%? No, that's too low, let's say 65%. The second is about a third of that, so that would be a bit more than 20%, uh, difficult to calculate it in my head, let's round up to 25%. The third also feels like a third of the first, but it is actually always a bit more than the second, so it should be 30%. Or even 35? No, let's go with 30. Oh, and I forgot that I have a fourth source, that only happens once a year, that should be really small compared to the others, so 5 or 10%? Probabaly 5 is closer, it isn't really that much". And so you end up with an answer of 65 + 25 + 30 + 5 = 125%.
Because people tend to be more aware of the relative size of the income parts to each other than of each part to the total, I would say that normalizing them is in order here, if you want to run some kind of numeric analysis on the income. I would only work with the actual reported numbers if the difference between people's beliefs and statements about their income and objective reality is an important topic for your work, for example if you are a psychologist studying cognitive biases, or if you are more interested in the self-perception of artists than in their economic circumstances.
Sadly, I don't have a good literature source to prove that it really works as I described it, it is just my personal empirical observation. But I don't think that reviewers will get caught up on this kind of decision, since, as the other answers said, there is no single "right" way to treat it. If anything, they will dismiss your whole data from this question as invalid due to a flawed querying technique. The best you can do is to preemptively acknowledge it and come up with arguments why your work is nevertheless useful and why the conclusions you are drawing are still good despite this specific source of inaccuracy in the data.
Comment: Once you have the normalized proportions, you can compare their distribution against the proportions given by people that were able to do the math. A difference in means that is statistically zero (for each of the income sources) would be convincing evidence that @rumtscho 's intuition is correct.
Answer: If social science has taught me anything, it's that if you give people a chance to give logically inconsistent responses, they will. So rest assured that there's nothing unusual about your subjects. This is something to keep in mind for designing future surveys. For the time being, it may be best to leave the responses as-is and just keep in mind in your analyses that the responses won't actually add up to 100%, as one would think. Rather than true proportions, you have noisy signals of how much income each subject gets from each category, so analyze them that way.
Comment: @Andrea That's an option. It's hard to say which is better, at least without a very concrete idea of what analyses you're doing, but consider that the pro of such a change is that you get proportions that actually add up, and hence perhaps better comparability between subjects, whereas the con is that you will obscure effects from the idiosyncratic ways people perceive and use numbers (e.g., 69% to 70% is seen as a more meaningful increase than 68% to 69%).
Comment: Thank you for your comment! Do you think it is better to leave as it is or, for example, normalize the percentage such that their sum is 100%. Considering the example reported, 53.85%and 46.15% (instead of 70% and 60%)?
Answer:
artistic activity, government support, private pension, activities not related with arts

Just at a glance, it seems that "artistic activity" and "activity not related with arts" should add up to 100%.
Of course "activity not related with the arts" is not the same as "not activity related with the arts," since there can be income associated with no activity at all.  But that's hair splitting that most artists won't notice.
If you assume that categories 1 and 4 should add up to 100%, and reinterpret those respondents accordingly, you may find that most of them have included categories 2 and 3 in with category 4.
However, all of this is data manipulation that is not ideal.  If you want accurate statistical answers, you must collect data that is accurate.  People might lie in response to your survey, and that's hard to guard against, but if people honestly trying to answer your questions can be in confusion over what is meant, your survey needs to be rewritten.
Next time proofread the survey for understandability, as well as ambiguity, before you send it out.
Answer: You have given four categories for income - what about income that is in none of them? For example, dividend income from holding stocks. It's not income from any form of activity, yet it's not government support or a pension either. I would suggest that in the absence of other information you should regard the responses as correct and attribute the missing money to sources that the respondents did not consider to be covered by the categories.
Comment: this doe not explain the case where the sum is above 100%
Comment: @Bob that is a good point, but I have already excluded that case as in most cases the sum is above 100%
Answer: Actually that is quite simple (and not even as illogical as you might think)! I assume that it is really the proportions of the different categories of income you are after by asking for percentages. So you can simply renormalize to 100%. In your example: if somebody says: 70% of my income is from artistic activities and 60% is from government support, this person (who has propably never had any training in working with percentages) is actually saying: the relative sizes or proportions of my income from artistic activities and government are about 70 to 60 or 7 to 6 (propably not realizing that percentages are supposed to add up to 100..). You can convert these statements about proportions to statements about percentages by simply renormalizing them, as follows: 70 / 130 * 100 = 53% artistic income, and 60 / 130 * 100 = 47% government support income..
(what I do here is actually take 130% as a "new" 100% and calculate the proportions..)
PS. this works for all cases where the sum of the stated percentages is unequal to 100
Hope this helps!
Answer: The majority of answers already given have already provided some insight into the obvious survey methodological flaws, so I will not dwell on that here.  Instead, I'll provide a few practical options on how to treat this data given that it's already collected and despite the flawed question. There are a few ways to handle this.  You could consider marking responses that did not meet your definition of a "valid responses" by treating the entire question as missing and then following any number of practices for handling item-nonresponse such as those discussed here.
You might also consider scaling each response so that the percentages add to 100.  Assuming each response is recorded as a percentage, this can be done by re-coding each original response $y_{{old}_{ij}}$ $(j=1,2,3,4)$ of the 4 sub-components to your question (i.e. artistic activity, government support, private pension, activities not related with arts) into a new response  $y_{{new}_{ij}}$ as follows:
\begin{eqnarray*}
y_{new_{ij}} & = & \begin{cases}
0 & ,\,\text{for}\,\sum_{j=1}^{4}y_{old_{ij}}=0\\
\frac{y_{old_{ij}}}{\sum_{j=1}^{4}y_{old_{ij}}} & ,\,\text{for}\,\sum_{j=1}^{4}y_{old_{ij}}>0\\
Missing & ,\,Otherwise
\end{cases}
\end{eqnarray*}
So for example, say you had a respondent $i$ who answered as follows:
<code> A. (i=1) Artistic activity:  10%
 B. (i=2) Government support: 0%
 C. (i=3) Private pension: 30%
 D. (i=1) Activities not related with arts:  40%
</code>
Then you'd recode as follows:
\begin{eqnarray*}
y_{new_{i1}} & = & \frac{10}{10+0+30+40}=\frac{10}{80}=12.5\%\\
y_{new_{i2}} & = & \frac{0}{10+0+30+40}=\frac{0}{80}=00.0\%\\
y_{new_{i3}} & = & \frac{30}{10+0+30+40}=\frac{30}{80}=37.5\%\\
y_{new_{i4}} & = & \frac{40}{10+0+30+40}=\frac{40}{80}=50.0\%
\end{eqnarray*}
Note that all the new percentages now add to 100%.  Whatever you do, please be sure you make any transformations very clear when reporting your results and I think @rolando2 provided some excellent advice on how to perform some sensitivity analyses to see how transformations like these might affect your conclusions.

How to treat illogical survey responses


What do ORs 'know'?

Question: It is often said that each node 'knows' the preceding and proceding nodes. But what identification information does the node have exactly? Just the IP address? Also, as a result of what protocol does it get that information.
Thank you!! :) :)
Answer: A node or onion router knows about other nodes what anybody can know. It's the public description of the network. It's the fingerprint, IP, exit policy and some configuration more, and the persistent public key. That's what it uses to encrypt data when sending it to the node.
A node obviously know who is connecting to it from the outside. It can decrypt the information that is encrypted with it's own public key: That is where the node should pass on that data it received.
It's as a result of the onion routing protocl, specified at https://gitweb.torproject.org/torspec.git/ and implemented in tor.

What do ORs 'know'?


Women attending Parshas Parah

Question: According to those opinions that say that Parshas Parah is a Torah obligation, do women have an obligation to attend, or would they be exempt for other reasons?
Comment: Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/74270/discussion-between---and-danf).
Answer: This site, citing Nitei Gavriel Purim 22:4 says:

Although women should make an effort to hear Parshat Para read in the
  synagogue, there is no true obligation for them to do so. Indeed, it
  is argued that women should be completely exempt from having to hear
  the Parshat Para reading because they were not involved in the sin of
  the Golden Calf.
Comment: For those of you wondering, the article addresses the link between the sin of the Golden Calf and Parah.
Answer: Nitei Gavriel (Purim 22:4, fn6) suggests (in addition to DanF's answer from Torah Musings) that women are exempt from hearing Parshas Parah for two reasons:

This obligation to purify oneself before Pesach is simply on the general public, not on women, and thus, individual women do not have to come and hear the Parsha
Even if it is, it would be considered a Mitzvas Aseh Shehazman Grama, as it is limited to a particular timeframe.

He does note dissenting opinions, see there for details.  I would also note that he adds earlier that most Acharonim don't Pasken that this is Deoraisa anyways.

Women attending Parshas Parah


Delete frequency components with FFT and IFFT

Question: I have a signal in Matlab defined by signal and t. As it is a noisy signal, I want to delete every component below a certain given frequency "x" Hz with the FFT. How could I do it? I guess the procedure is FFT the signal, delete those components and then apply the IFFT, but I don't know how to implement it. Any help is appreciated!
Answer: In fact, deleting a certain frequency range from the FFT equals settings these frequency components to zero. Hence, you end up with the following code:
N = 1000;
signal = randn(N, 1);

N_clear = 490;

% Remove the calls to fftshift, if you want to delete the lower frequency components
S = fftshift(fft(signal));
S_cleared = S;
S_cleared(1:N_clear) = 0;
S_cleared(end-N_clear+2:end) = 0;
S_cleared = fftshift(S_cleared);

signal_cleared = ifft(S_cleared);

subplot(2,2,1);
plot(signal);
title('input signal');

subplot(2,2,2);
plot(abs(S));
title('input spectrum');

subplot(2,2,3);
plot(abs(S_cleared));
title('output spectrum');

subplot(2,2,4);
plot(signal_cleared);
title('output signal');

As you can see, the input signal is very quickly varying. Then, after filtering out almost all higher frequency parts, you end up with a smooth signal.
Note, that normally you use FIR/IIR lowpass/highpass filters for realtime-signal processing, because the FFT is block-based and cannot produce nice transitions between the processed blocks.
Comment: That's perfect, but what do you mean with `N_clear`? If I want to delete frequency components below 1Hz, knowing that f=k*fs/N, with a given sampling frequency, N the length of the signal and k a vector of the length of the signal, I should delete every component k that is under 1Hz from the S vector? Thanks for the answer! @maximilian-matthé
Comment: N_clear is the amount of frequency bins you want to erase. Sure, you can relate this to the actual physical frequencies with the formula you provided.
Comment: @MaximilianMatthé, I want to filter out all the frequencies above 80 Hz from my signal. In this case what is N_clear? How should I modify the code to filter out all the higher frequencies? Thank you.


Can I unsubscribe from comments to my answers?

Question: Is there a mechanism that allows me to "unsubscribe" from comment notifications on my answers? Ideally something that operates on a per-answer basis. Alternatively, can I mute certain people so their rants do not result in a notification?
Comment: You can't block people or disable comments yourself. If someone is ranting on your posts, flag the comments for a mod to look at, if it is that bad the mod can disable comments or take appropriate action.
Comment: @matigo that _is_ breaking rules. Comments are for asking for clarification on a question and answer and are absolutely not for having discussions. Please flag such comments for mod attention so they can be deleted or moved to chat.
Comment: This is unfortunate. The comments are not breaking any community guidelines, so flagging them would waste people's time. I'll just have to continue ignoring asinine arguments about Software X vs. Software Y from people who are so uptight that it's impossible for them to shrug their shoulders and move on
Comment: @matigo Ignorance is bliss
Answer: There isn't a way to turn off notifications for comments on your posts. I've personally found a long series of comment notifications unwelcome on a few occasions. But I guess I am glad they can't be disabled since comments sometimes convey very important information.
The general attitude towards comments on SE is that they exist to help people work towards improving posts, though they do sometimes have some other kind of value. Once the improvement to the post has been effected, comments ought to be no longer needed. They are considered to be of transient value at best (though a substantial minority at least are worth keeping around).
Because of this philosophy of comments, it is felt that they may be removed casually. If a person has something of lasting importance to share, they had better put it into a post.
So, you should not hesitate to flag comments that are not of value. Comment flags are rarely declined. One of the things I try to do every time I visit any question or answer on Ask Ubuntu is scroll through the page looking for comments that can be cleaned up.
NB: This doesn't apply to meta, which, unlike the main site, exists in part to allow and preserve discussion. It's rarely desirable to remove comments on meta. However, if someone is trolling you with comments on meta do go ahead and flag.
Comment: @matigo no, the system only cares about posts. We won't get any flags about deleted comments :)
Comment: Is there any penalty for deleting comments? If comments are generally considered ephemeral, then I can write a script that can clear out my comments after a set period of time. However, if that flags my account for "suspicious activity", then I would refrain …


Are there examples of backward time travel in the talmud and/or midrash?

Question: The gemarah discusses a story where Moshe is taken to see the lecture hall of Rebbi Akiva and the midrash discusses God showing Adam ensuing generations and their scholars. I would like to know if there any examples of backward time travel, where someone living at a later chronological date is shown or taken to an earlier time.
Comment: When you say "shown or taken to",  do you mean something more than "told about or taken to"? Otherwise, there are many times when later people have been told about earlier people. By that I mean - to answer this question properly, by what criterion should one judge a _midrash_ as backward time travel and not recounting?
Comment: Re Adam, are you referring to the _g'mara_ about his ability to see "from one end to the other"? http://www.sefaria.org/Chagigah.12a?lang=bi
Comment: @WAF I mean visually shown either by causing the scene to appear in front of him (a la Yaakov seeing Shimshon, thinking he was Moshiach and then seeing him die, all in a vision) or by taking the person into the scene as with Moshe and Rebbi Akiva's classroom. The Adam reference is from Avoda Zara 5a (see also https://books.google.com/books?id=qWj96h2n2HAC&pg=PA58&lpg=PA58&dq=adam+was+shown+each+generation+and+its+expounders+and+supporters&source=bl&ots=kRp3P3PO_T&sig=ymBS33TFAIvpOEybS-iKpdDH4dQ&hl=en&sa=X&ved=0ahUKEwiujOqLrP7PAhXKxYMKHWZNCYAQ6AEIHDAA#v=onepage)
Comment: Wouldn't it be unnecessary?
Comment: related: https://scifi.stackexchange.com/questions/75839/first-use-of-time-travel-in-fiction
Answer: Almost...
תענית כה א

רבי אלעזר בן פדת דחיקא ליה מילתא טובא עבד מלתא ולא הוה ליה מידי
  למטעם...חלש לביה ונים אזול רבנן לשיולי ביה חזיוהו דקא בכי וחייך ונפק
  צוציתא דנורא מאפותיה כי אתער אמרו ליה מ''ט קבכית וחייכת אמר להו דהוה
  יתיב עמי הקב''ה ואמרי ליה עד מתי אצטער בהאי עלמא ואמר לי אלעזר בני
  ניחא לך דאפכיה לעלמא מרישא אפשר דמתילדת בשעתא דמזוני אמרי לקמיה כולי
  האי ואפשר אמרי ליה דחיי טפי או דחיינא א''ל דחיית אמרי לקמיה א''כ לא
  בעינא...

Taanit 25a
R' Elazar Ben Pedat was very poor, he went through blood-letting and had nothing to eat...he felt weak and fell asleep.
The Rabbies came to ask him questions, and saw him laughing, crying and then a flare of fire came out of his forehead.
When he woke up they asked him - why did you cried and laughed?
He answered, God sat with me, and I asked him, until when I will suffer in this world?
He replied: Elazar my son, do you want me to reverse the world to it's beginning? maybe you will be born in time of prosper.
I said: just maybe?! Did I past half of my life time? He said: you did.
I said: If so, I don't want...
Answer: Not an example of backward time travel in the sense of someone at a later date being taken back to an earlier time, but the Sefas Emes (Purim 5637) writes that the salvation of the Jews was through Vashti's removal at Achashverosh's feast, even though the punishment of Haman was a result of the Jews eating from Achashverosh's feast. This is because God knew that the Jews would repent through love (teshuvah me-ahavah), and therefore, their sins would become merits. Thus, although it was a sin for them at the time that they partook of the feast, in retrospect it was a merit and in fact the source of their salvation.
Also not an exact match, but according to the Maharam Chalavah and a number of other sources, we recite a bracha on the miracle of leaving Egypt, even though the bracha recited on a miracle extends only two generations, because on the night of the Seder it is considered as if we ourselves left Egypt. This might also be the reason for Hallel at the Seder, which seems not to be the ordinary Hallel of Yom Tov, but Hallel on a miracle, which we can recite because "we ourselves left Egypt." Thus, the halachah that we are to see ourselves as having left Egypt has practical ramifications in other realms and may be considered a communal obligation to engage in (metaphorical) time travel.
Comment: @Jonathan An answer which actually has someone literally going back in time, like the OP asked for.
Comment: So...this doesn't actually answer the question then?
Comment: @DonielF What did you expect? Hehe.
Comment: I don't think one exists. I know that the Talmud talks about people going forward but never backwards.
Comment: Is there any reason why the Sefat Emet adds anything beyond גדולה תשובה שזדונות נעשות כזכויות or why the Maharam Chalava application adds anything beyond חייב אדם לראות את עצמו כאילו הוא יצא ממצרים? These are just applications of the Mishna and Talmud (not to say that the Mishna and Talmud themselves aren't time travel)
Comment: Its interesting that the Sfas Emes writes that it was a teshuvah m'ahava, seemingly from the gemara megillah 14a, it was very clearly a teshuvah m'yirah


Linux CRC Error

Question: I'm getting an error when trying to boot from live Ubuntu cd. "Uncompressing Linux... crc error -- System halted". I've also tried this using a Linux mint live cd, same error. Is this something related to the MB?
Answer: According to this the kernel doesn't like itself. Based on what you've said, I feel like your hard drive might be to blame. Is it old? Do you have a spare to test on?
Answer: If you can, try the live cd on another computer, or a different cd rom in the same computer.
If you can't do either of those, I'd try installing from a flash drive.
I think that a flakey cd drive is more likely than the motherboard. You can also try a memory test, live cd here or some Ubuntu live cds have it on there.
Motherboard problems could in theory be an issue too, but I've never seen it, so I'd try the above first.

Linux CRC Error


Why does this rescue group want to talk to my vet?

Question: In filling out the application to take a new animal, the rescue group asks for information for my current veterinarian. Why do they want that information and what will they ask/tell my veterinarian?
Answer: First we want to know that you have thought about your pets medical needs.  And your vet probably has a pretty good idea of how you treat your pets.  Do you bring them in for regular check ups, get them vaccinated, and provide heartworm prevention treatment regularly?  When they come it are they clean well groomed, and not showing signs of neglect?  Your vet is probably not going to tell us all of that but the vet may be able, based on that information, judge if you treat your pet decently or not.  When we call we hope that the vet will let us know that he sees your pets regularly and be comfortable with your adopting another pet.
I have never had a vet tell me that someone would not be a good choice to adopt, but I have had one say that he did not have an opinion.  That was not necessarily a problem but it did lead us to investigate deeper.  But a good vet reference goes a long way towards comforting us that you will be a good pet parent for this animal that we have invested time in rehabing and saving.
Answer: If you are adopting from a breed specific or species specific rescue the goal may be to see if your current vet specializes in the pet you are considering adopting. A breed or species specific rescue is going to know who the best vets in the area for addressing the special needs of your new pet.
If your current vet is not one of the local vets who specialize appropriately, they will likely suggest an alternative. This is particularly true if you are adopting a special needs pet.


How to determine scope and applicability of a passage, with focus on John 6:32-51?

Question: What is the scope of the bread of life discourse in John? I have always, along with most commentators I've read,  thought it was universal because of terms "world" (33, 51), "he who" and "anyone" (35, 37, 40, 45, 47, 50, 51), and "no one" (vs. 44). However, I've read some comments that when Jesus talks about folks coming to and believing him in this passage, he is not referring to new followers or humanity in general, but only to God-fearing Jews and Gentiles at that time period, before his crucifixion, who God was pointing toward Jesus.  Does that argument have weight or should we refute it on some hermeneutical premise? So, there is a general question behind my specific one: how does one exegete scope and applicability?
Thanks-
Comment: If Jesus stood for crucifixion of the flesh through fasting, then Jesus as "the true bread coming down from heaven", ment to fast first thing in the morning (Ecc 10:16). And when Jesus said "eat my flesh, because my flesh is true meat", he could have referred to evening fasting. Because, the Israelies collected the manna in the morning, and the meat in the late afternoon (Ex 16:12).
Answer: The scope and application would be, as you alluded,universal to the whole world.Yes, He is referring also to new followers in the future, such as Paul was.
The scripture says in John 10:35 If he called them gods, unto whom the word of God came, and the scripture cannot be broken;
Also in John 17:20 Neither pray I for these alone, but for them also which shall believe on me through their word;
The Bread is offered unto all men, but it must be mixed with faith. There were many that heard:
John 6:66 From that time many of his disciples went back, and walked no more with him.
One reason that you are hearing opposite opinions all boils down to the long debate of Calvinism versus Armenianism.
If it was not meant for the whole world, then there would be no basis of punishment for not believing.
Answer: I realize that I am alone in this but I believe John uses the word κόσμος 78 times to refer to the then contemporary Jewish theocracy aka Israel, God's chosen "People":

[Amo 3:1-2 KJV] 1 Hear this word that the LORD hath spoken against you, O children of Israel, against the whole family which I brought up from the land of Egypt, saying, 2 You only have I known of all the families of the earth: therefore I will punish you for all your iniquities.

Amos the prophet, like all the prophets speaks of God's coming visitation on Jerusalem, the temple and the Jews:

[Amo 3:1 KJV] 1 Hear this word that the LORD hath spoken against you, O children of Israel, against the whole family which I brought up from the land of Egypt, saying,
  [Isa 46:3 KJV] 3 Hearken unto me, O house of Jacob, and all the remnant of the house of Israel, which are borne [by me] from the belly, which are carried from the womb:
  [Hos 4:1 KJV] 1 Hear the word of the LORD, ye children of Israel: for the LORD hath a controversy with the inhabitants of the land, because [there is] no truth, nor mercy, nor knowledge of God in the land.
  [Hos 5:1 KJV] 1 Hear ye this, O priests; and hearken, ye house of Israel; and give ye ear, O house of the king; for judgment [is] toward you, because ye have been a snare on Mizpah, and a net spread upon Tabor.
  [Jer 31:1 KJV] 1 At the same time, saith the LORD, will I be the God of all the families of Israel, and they shall be my people.
  [Jer 33:24-26 KJV] 24 Considerest thou not what this people have spoken, saying, The two families which the LORD hath chosen, he hath even cast them off? thus they have despised my people, that they should be no more a nation before them. 25 Thus saith the LORD; If my covenant [be] not with day and night, [and if] I have not appointed the ordinances of heaven and earth; 26 Then will I cast away the seed of Jacob, and David my servant, [so] that I will not take [any] of his seed [to be] rulers over the seed of Abraham, Isaac, and Jacob: for I will cause their captivity to return, and have mercy on them.
  [Amo 2:10 KJV] 10 Also I brought you up from the land of Egypt, and led you forty years through the wilderness, to possess the land of the Amorite.
  [Amo 3:2 KJV] 2 You only have I known of all the families of the earth: therefore I will punish you for all your iniquities.

The time of their visitation was the time of Messiah, in the first century:

[Isa 10:3 KJV] 3 And what will ye do in the day of visitation, and in the desolation [which] shall come from far? to whom will ye flee for help? and where will ye leave your glory?
  [Jer 8:12 KJV] 12 Were they ashamed when they had committed abomination? nay, they were not at all ashamed, neither could they blush: therefore shall they fall among them that fall: in the time of their visitation they shall be cast down, saith the LORD.
  [Jer 10:15 KJV] 15 They [are] vanity, [and] the work of errors: in the time of their visitation they shall perish.
  [Jer 11:23 KJV] 23 And there shall be no remnant of them: for I will bring evil upon the men of Anathoth, [even] the year of their visitation.
  [Jer 23:12 KJV] 12 Wherefore their way shall be unto them as slippery [ways] in the darkness: they shall be driven on, and fall therein: for I will bring evil upon them, [even] the year of their visitation, saith the LORD.
  [Jer 46:21 KJV] 21 Also her hired men [are] in the midst of her like fatted bullocks; for they also are turned back, [and] are fled away together: they did not stand, because the day of their calamity was come upon them, [and] the time of their visitation.
  [Jer 50:27 KJV] 27 Slay all her bullocks; let them go down to the slaughter: woe unto them! for their day is come, the time of their visitation.
  [Jer 51:18 KJV] 18 They [are] vanity, the work of errors: in the time of their visitation they shall perish.
  [Hos 9:7 KJV] 7 The days of visitation are come, the days of recompence are come; Israel shall know [it]: the prophet [is] a fool, the spiritual man [is] mad, for the multitude of thine iniquity, and the great hatred.
  [Mic 7:4 KJV] 4 The best of them [is] as a brier: the most upright [is sharper] than a thorn hedge: the day of thy watchmen [and] thy visitation cometh; now shall be their perplexity.
  [Luk 19:44 KJV] 44 And shall lay thee even with the ground, and thy children within thee; and they shall not leave in thee one stone upon another; because thou knewest not the time of thy visitation.
  [1Pe 2:12 KJV] 12 Having your conversation honest among the Gentiles: that, whereas they speak against you as evildoers, they may by [your] good works, which they shall behold, glorify God in the day of visitation.

The fourth gospel is a Jewish account of the Jewish messiah interacting with the doomed Jews of his generation, just like the other gospels.
For example:

[Mat 23:33-38 KJV] 33 [Ye] serpents, [ye] generation of vipers, how can ye escape the damnation of hell? 34 Wherefore, behold, I send unto you prophets, and wise men, and scribes: and [some] of them ye shall kill and crucify; and [some] of them shall ye scourge in your synagogues, and persecute [them] from city to city: 35 That upon you may come all the righteous blood shed upon the earth, from the blood of righteous Abel unto the blood of Zacharias son of Barachias, whom ye slew between the temple and the altar. 36 Verily I say unto you, All these things shall come upon this generation. 37 O Jerusalem, Jerusalem, [thou] that killest the prophets, and stonest them which are sent unto thee, how often would I have gathered thy children together, even as a hen gathereth her chickens under [her] wings, and ye would not! 38 Behold, your house is left unto you desolate.

Or as Peter said:

[Act 3:24 YLT] 24 and also all the prophets from Samuel and those following in order, as many as spake, did also foretell of these days.

So no, the bread of life account in John 6 is not about "the Church" (the faith without works body of Christ that Paul was sent to found by the risen Christ.

So what is John 6 actually about? John is comparing the Jerusalem Jews (except for the elect Jews) to the Jews who died in the wilderness because of unbelief and did not enter the promised land:

[Heb 3:15-19 NKJV] 15 while it is said: "Today, if you will hear His voice, Do not harden your hearts as in the rebellion." 16 For who, having heard, rebelled? Indeed, [was it] not all who came out of Egypt, [led] by Moses? 17 Now with whom was He angry forty years? [Was it] not with those who sinned, whose corpses fell in the wilderness? 18 And to whom did He swear that they would not enter His rest, but to those who did not obey? 19 So we see that they could not enter in because of unbelief.

He came unto his own but his own did not receive him. But, as Paul says, an elect remnant did receive their messiah:

[Rom 11:7 NKJV] 7 What then? Israel has not obtained what it seeks; but the elect have obtained it, and the rest were blinded.

Israel was born when they were delivered from Egypt. Israel's rebirth was when the messiah led out "the Israel of God", the new covenant Jews who were miraculously raised from spiritual death by the outpouring of God's spirit in the last days.
So like all of the law, the prophets and the writings prior to Paul (including the Jewish letters of the NT) the gospels are about the Jews rejecting their messiah and incurring the wrath of God end the end of their unique relationship to God.
When you read Paul's writings they are speaking to the believing saints, elect Jews and gentiles.
Answer: Considering the purpose John gives for his gospel:

Now Jesus did many other signs in the presence of the disciples, which are not written in this book; but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name. (John 20:30–31, ESV)

and John's additional statement:

Now there are also many other things that Jesus did. Were every one of them to be written, I suppose that the world itself could not contain the books that would be written. (John 21:25, ESV)

John has a specific reason for what he included in his gospel.  Given John's reason, why would he include the discourse in 6:31-51 if it didn't have a universal application?


What happens if someone gets my seed phrase?

Question: If someone happens to get my seed phrase (off a paper I wrote it on) can they restore my Daedalus wallet on another machine and take my ADA?
Answer: The seed phrase is used to generate your private keys (and thus your public keys as well). If someone has access to your seed phrase, they can "restore" your wallet Yoroi, Daedalus, or any other wallet application and can do anything with your wallet that you could do. The only way to know if this has happened is to notice any transaction sending Ada or a token from your wallet that was not done by you. If you have any doubt, just create a new wallet and transfer all of your tokens and then funds from your old potentially compromised wallet to your new wallet.
Answer: As others have stated, yes they can restore your wallet and yes they can take all your ada and anything else associated with it.
With that said, here are some tips for securing your mnemonic phrase.
1.) Do not store these phrases on a computer. And if you must, do it on a air-gapped machine.
2.) Make sure you protect yourself from natural disasters. For example what if your house burns down, burning your computer with the restored wallet as well as the piece of paper the mnemonic was on? I personally stamped mine into a metal plate and keep it in a fireproof safe.
3.) Make sure you include instructions in your safe for a what to do with it in case you die. Personally my family does not know much about crypto so I would want my beneficiaries to have instructions on what to do. This way a loved one gets those gains in case something were to happen to you.
4.) Bonus tip, get a hardware Wallet like a Ledger X. This insures that your keys are not compromised in the making of your wallet. Although probably unlikely, it is possible that your internet connected device, you make the wallet on, is compromised. If it is, there is a possibility your wallet is too.
Answer: Yes. If someone get your seed phrase, he will be able to steal all your funds.
Answer: If someone receives your mnemonic phrase or master private key, they can access your funds and instantly transfer all your ADA and tokens to their personal address.
Try not to make common mistakes and your funds will always be safe.
Answer: In Hierarchical Deterministic (HD) Wallet the seed phrase is used to generate a serie of public (and its correponding addresses) and private keys pairs (accounts).
A specific seed will always generate the same set of pairs.
If someone accesses your mnemonic, he will be able to generate the private key for the account containing the funds (usually the first account derived). With the private key, he will be able to sign a transaction and steal the funds.
Answer: In addition to securing your seed phrase using the above methods, you may also want to memorise it. You can do that by grouping it sets of maybe four and creating silly sentences each containing four of the words. Every three days, write down the sentenses while highlighting the keywords. Do that for some months and it sticks.
This way, if I ever need to move my funds in an emergency (like suspecting someone may have had access to the physical backup), I can move fast by downloading a wallet anywhere and importing the wallet from my memorised seed phrase and moving the funds.


Changing font of an entire Google Slides presentation

Question: Is there a way to change the font of an entire Google Slides presentation all at once? If not, this would be a very nice feature to have, and I suggest that google add it. [Note: I am not asking about how to change the default font, because that does not apply to existing text.]
Answer: Yes, there is, by using the Google Sheets API. Maybe the easier way to use it is by using Google Apps Script.
It's possible that there is a Google Slides add-on that does this. If it already exists, you could find it from the Google Slides toolbar by clicking on the Addons menu then on Get addons.
Comment: Thanks for that information, but I was hoping it would be easier than that. If anyone happens to know which addons can do that, that would be nice to know so I don't have to just try them at random. It's not really a priority for me, but I'm having the hardest time deciding whether I prefer Times New Roman (serif) or Arial (sans serif), and it would be nice to be able to switch effortlessly back and forth!
Comment: I think that you should edit your question to add more details. I.E. i didn't mentioned that Google Slides themes / master slides that might be helpful if you are open to change your how do you create presentations (assuming that you usually add text shapes rather than using slides layouts)
Answer: Go to View -> Master and change the font in the master slide.
Answer: Go to slide -> edit theme and then Command + a (or just go one by one) and change the font
This will change add the font to the theme and all the slides.


5 Day marinated chicken breast

Question: Bought chicken breast on Sunday and put in marinade.  It is now Thursday.  Chicken has turned a bit white . . . is it safe to cook and eat at 5 days in marinade?
Comment: What's in your marinade? If it contains any acid (lemon juice or vinegar), the surface may have just "cooked" due to the acid.
Comment: Beside that official word on food safety I linked, we have some questions on marinade duration, they can be found through the search
Answer: 2 days is usually the max for chicken in the fridge that is officially recommend, 5 days is definitely on the long side.  Pending the sell by date that the chicken had originally.
Color is just the marinade, it's the bacteria you need to be concerned about.  Hard to tell if chicken has gone bad in a marinade.
Good acidic or high salt marinade, you are probably safe.   Really up to you if you want to take the small risk or just throw away.

5 Day marinated chicken breast


Can I use copyrighted music in my video game, even though it's free to play?

Question: I'm making a video game, and thought of making a boss theme, where I use an 8bit remix and the original instrumentals of the song Chop Suey. I'm already in contact with the 8bit versions creator, but I'm not sure if I can use the original instrumental, without my game being taken down.
Answer: You need permission to use the work in your game. Just because a work (like a song) is freely available for you to play/use does not mean that also have the right to re-distribute the work yourself. You need to specifically seceure the right to use the work in your game from the person or entity that holds the intellectual property rights.
Music in particular is interesting, as both the composition and the performance are subject to intellectual property laws. You generally need to secure the rights from both parties (if they differ), in order to use an existing recording of the song.
Comment: So i just need permission from both creators, right?


How do I get deep blacks on print?

Question: I bought a Pixma ip8750 to try and make my first steps in printing. It does print in hexachromy, so it has a grey, a dye black and a pigmented black. However the results I am getting in b&w prints are far from good. Just the glossy photo paper had a decent result, while matte coated paper (300gr) were greenish or with a touch of magenta, depending on if I choose common paper or matte photo paper in the printing menu.

Could this depend just on the paper type? Just glossy paper has good blacks, or am I doing something wrong?
Comment: what colour are you using for black? Specifically, are you using a rich black?
Comment: For your reference, [here's an article on Rich Black](https://en.wikipedia.org/wiki/Rich_black)
Comment: If I use the eyedropper tool on the black I see the values C75 M68 Y67 K90. I dont know what is a rich black and I also dont know if the printer is using normal or pigmented black but I assume pigmented as the level of the ink decreased quite more
Comment: I have the same problem.
It's impossible to print a flyer with a black background that actually is black. It turns out in a vague purple. I managed to get this printed in black using plain paper, standard quality, and "fit to media" settings. However, as soon as I try to print in higher quality (borderless, photo glossy paper, etc..) the same thing happens, it's palish violet back again.
Answer: The only suggestion I can give is to go to your printer options in your operating system and experiment with the different paper stock options. Also experiment with the color calibration in the printer options if they are available to you.
I'm honestly not surprised that only glossy paper had decent results.
I'm making a big assumption here from looking at Epson's website for this printer that when they claim it is "Ideal for photo enthusiasts" that you should be using glossy or photo paper for high quality print. Your matte coated paper might just not be good enough.
From personal experience with various printers I find that the choice of paper stock makes a huge difference with the correct settings.
You basically need to experiment a lot because every printer is different and it has in the past taken some experimenting to get closer to the results I need with a new printer.
Answer: Two things I would have tried:
First: I recommend to convert black and white photos to greyscale. That way you avoid a color tint, but on the other hand the result might not be as dark as you want to. I don't know how your printer works, but with the additional black and grey colors, I'm guessing there is a possibility to use them in a greyscale scenario to get a satisfying result.
Second: Adjust the color of the image so that the darkest part is close to CMYK 30 20 20 100 (more Cyan than Magenta and Yellow to avoid a brown tint) do a test print and adjust CMY from there until the darkness and tint is to your liking. It can be hard to adjust that in a photograph, so another solution can be to adjust the levels in your printer, either via a control panel or in the driver settings. Again, I'm not familiar with the printer, so consult your manual.
The color of the paper will affect the color. Coated paper (gloss) will give you a darker and clearer result because the colors are not absorbed, but stays on the outside and the paper reflects more light. Uncoated will absorb more color and the print looks less saturated, or faded, in lack of a better term. A similar effect can also be seen on coated matte paper.
Do not use registration black for anything else than registration marks. Anything above 300 % cover is not recommended, it will "never" dry and you might get smudges or a metallic effect on the darkest parts.
Answer: First make sure you're outputting the darkest black possible.
From the link above I would try Registration black which is 100% of all the colors.
Secondly yes paper coating makes a big difference in appearance. Glossy photo paper has a clay coating that can absorb a lot more ink than plain paper. With that print setting the printer puts out more black and the medium absorbs more black.
Any Paper besides glossy photo paper makes photo prints look not as good and lighter. Medium gloss, "frost" "Lustre" or "semi-gloss" can produce good results at less cost.
Comment: HI, if the black print on the right came out of your printer than we know it is outputting dark black. It would now be the printer or the paper causing problems. All photo papers have some coating. Glossy photo paper makes colors look bright and shiny. The coating allows it to be sharp, rich and bright. Your printer is not off the hook though. If you put photo gloss paper in your printer and its expecting regular laser print paper it will give a lot less ink. The best option is to use the paper specified in your printer settings. If Pixma doesn't make paper than find what manufacturers it uses
Comment: If you can import HP or Epsom or some common printer/paper manufacturers settings into your printer you can specify (for example) HP premium photo Paper setting and then use HP premium photo paper to be sure of a match from the RIP.
Comment: So basically my printer has nothing wrong and i should try with some coated paper? Where I used to go they had a paper which didnt look shiny but the colors were brighter and kind of glossy. Is coated paper glossy paper or glossy is just the photographic ones?
Answer: HELLO so i was having the same problem with my canon pixma 3770 . i was using matte sticker paper for stickers. the blacks were coming as purpleish or redish not pure black. so i played with everything the main windows printing app and the canon apps so i got the pure black by using canan easy photo-print app
the details were
paper size- letter: 8.5"x11" (22x28cm)
media type - plain paper
every other option off .
print quality - high
and boom there you go. tell me if this helps anyone.

How do I get deep blacks on print?


Error during ati radeon x600 driver

Question: I get this error message during installation.
Answer: Don't worry about installing the AMD graphics drivers. The open source drivers that come with Elementary OS are the best AMD graphics drivers. What you are trying to install is too old and no longer supported.
You may also update your kernel and see how that works for you.
Alright, buckle up your big boy pants because you are going balls deep today!
We get to play with the terminal. This guide is made assuming that you can get to the terminal [(edit) and the Desktop GUI.] Here is a list of commands that will set you up and upgrade your kernel.
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install software-properties-common
sudo apt-get update
sudo add-apt-repository ppa:teejee2008/ppa
sudo apt-get update
sudo apt-get install ukuu
sudo apt-get upgrade

Now go ahead and use UKUU to update the kernel to 4.11.3
It will say that there are errors the first time you try this, ignore
that.
Reboot your computer.
Go back to UKUU and reinstall 4.11.3 kernel
If the install was successful, go ahead and restart your computer
again.

Now run
sudo apt-get purge ukuu
sudo apt-get update
sudo apt-get upgrade
If you only have access to the terminal use this advice given from Lemonslice
As a workaround, you might want to try to install 4.11 from the Ubuntu mainline kernels.
You can download and install from http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.11.4/ the following packages:
sudo dpkg --install linux-headers-4.11.4-041104_4.11.4-041104.201706071003_all.deb \
linux-headers-4.11.4-041104-generic_4.11.4-041104.201706071003_amd64.deb \
linux-image-4.11.4-041104-generic_4.11.4-041104.201706071003_amd64.deb

Now restart your computer when your kernel is installed and continue on.
sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt-get update
sudo apt-get -f install
sudo apt-get install gcc-6 g++-6
sudo apt-get update
sudo apt-get upgrade

Now reboot your computer again for good measure.

When you computer has restarted go ahead and run
sudo apt-get autoremove

Say yes to any prompts.
Reboot your computer and now try your multimedia keys and possibly
your video drivers.

I have to do this for my laptop and desktop for it to fully function. The 4.11.3 kernel is really good and has not given me issues.
So yeah, it seems like a lot, you can do it. Have confidence!
Comment: It seems that source drivers dont work very well. Videos showing weird lines. Is there any current driver?
Comment: Its like videos loosing frames . Doesn look smooth...
Comment: Updated my answer. Try updating the kernel.
Comment: I instralled  4.11.3 kernel without any problems. However this did not fix the issue!

OS: elementary OS 0.4.1 loki
Kernel: x86_64 Linux 4.11.3-041103-generic
Uptime: 7m
Packages: 1971
Shell: bash 4.3.48
Resolution: 3840x1080
WM: Mutter(Gala)
WM Theme: elementary
CPU: Intel Core2 Quad CPU Q9400 @ 2.668GHz
GPU: AMD/ATI RV370 [Radeon X600/X600 SE]
RAM: 1304MiB / 7981MiB
Comment: As soon as i view one youtube video my cpu goes wild from 67-86%
Comment: That could be dependent on your browser. I use Chrome, what do you use? Otherwise, try it on Firefox.   sudo apt-get install firefox

Error during ati radeon x600 driver


Can Hostelworld Gold membership numbers be shared among multiple accounts?

Question: Is a Hostelworld Gold membership locked to one particular account, or can it be used when make booking from separate accounts to get a discount? If the latter, then does Hostelworld invalidate cards that are shared by 'too many' accounts?
Comment: A question that could be answered easily by someone who has a gold card (I keep getting free ones through promotions they run), but don't want to have my card invalidated trying to test this. :p
Answer: I don't have a Hostelworld membership, but I emailed them to see what the official stance is (without anyone risking getting their card invalidated).
From Louise Clark on the customer service team:

Thanks for your email.  Gold Cards are registered to one email address so all bookings made with that address will be automatically discounted.
  You can also enter the Gold Card number when using a different email address and the discount will still apply.
  This is not limited to a certain number of email addresses.

So it looks like the answer is: enter in the membership number on as many bookings as you'd like from as many email addresses you'd like. :) Happy traveling!
Comment: awesome! I'd tweeted them but without response.  So @Ankur...care to share your gold card number then? ;)


If I've lost my wallet, but know my bitcoin receiving address, can I get my bitcoins back?

Question: Although I do have a backed up wallet file, I seem to also have a second bitcoin receiving address, which doesn't seem to correspond to it. Is there a way to recover any coins associated with that receiving address, or are the coins lost forever?
Comment: How did you lose your wallet? This might help us if #2 in my answer below applies.
Comment: How recent was that wallet backup.  Within the past 100 transactions (incoming / received) that you've had?
Comment: I had to refresh my computer do to updates and all my installed software such as bit coin wallet was gone after the process. I did back up my wallet almost everyday and also I did it on a external hard-drive,
but when I re-instal the bit coin wallet from bitcoin.org it give me a new receiving address and even if I have all back -up data and my previous receiving bit coin wallet where all my bit coins I have purchased were I do not know why is it not showing it in my new wallet. I have tried to recover and open my back up wallet files but it does not show my bit coins.
Please help. I did watch
Answer: You can't get your bitcoins with just the receiving address (if that could be done, they could easily be stolen), so your only chances of retrieving them are:

If they're stored in the wallet file you have backed up, then you can use that
Somehow recovering the original wallet file, which is a data recovery exercise. This might be possible in the case of a failure or deletion of a hard disk, or a deletion from an SD card/memory stick
Answer: It sounds like you have an old wallet backup that does not have the private key to the public address you are looking for. You are probably in the realm of data recovery.
I wrote a blog article that might help: http://gary-rowe.com/agilestack/2012/08/17/how-to-recover-your-bitcoins-from-a-failed-hard-drive/
Comment: And it should be made clear, ... if this was enough money to worry about -- STOP USING THE COMPUTER which had the wallet before it was lost/damaged/corrupted/etc. Chances of recovery may diminish each time your computer does anything to the hard drive.


Some feelings about Testing Engineer and Software Engineer in Agile development?

Question:
I am Software developer, have worked for Agile development in some years. In theory, team members should support together. But the reality is different,I always struggle with Testing Engineers about the scope between us.

Testing Engineer usually force developers to write unit test, must have 80%-90% test coverage. I don't know why 80%-90%? Why they don't write unit test?
Should they provide the solution in coding to improve ability to testability or improve quality? and How?
They always be happy and then complains about the bugs? However, If the software have no bug, I feel they are unhappy

Please feel free sharing your experience
Answer: Why don't test engineers write unit tests?
There are several reasons developers are usually tasked with creating unit tests:

Developers are intimately familiar with the code they are writing. They understand what that code is intended to do and more importantly why that specific implementation was chosen. Ideally they are writing the unit tests while or before the code is written.
Test specialists (whether they are called testers, QAs, test engineers or something else) are broadly familiar with the application as a whole. They may not have as much experience with code as developers, nor are they necessarily aware of the underlying logic that's needed.
While testers can write unit tests, it is usually a less effective use of their time, since the ideal time to create unit tests is before or during application development - a time when testers often aren't involved with whatever part of the system is being built.
The proper time to run unit tests is whenever and wherever the application is compiled. Testers often don't have the authority to check in code to the main application, and they often don't have the ability to add to tests being run in whatever continuous integration system is being used.
There are usually more developers than testers, leading to functional testing often becoming something of a bottleneck.

Should testers provide code to improve testability and quality?
Ideally testers should provide suggestions to improve testability and quality. Those suggestions may not be the best way to improve testability or quality, because as I said above, testers are less familiar with the application code and architecture than developers.
Testers can certainly work with developers to:

Suggest tests a developer may not have considered
Request specific information be surfaced in the application to allow for easier integration and functional automated tests (for instance, if the application architecture dynamically generates HTML Ids, a tester can request developers use a different attribute to provide a unique reference to each element on a web page)
Use information on unit tests to effectively improve coverage by minimizing overlap (for instance, when business logic is thoroughly unit-tested, integration tests do not need to cover all possible business logic paths, but can focus on ensuring that the correct information is passed from module to module)

Should testers be unhappy if they don't find bugs?
Yes
All non-trivial software has bugs. Software is complex, and the number of paths through a piece of non-trivial software is if not actually infinite, then so large that testing every possible path is impossible. Even with something very simple, like a basic text editor, users can add text and delete text they added as often as they please. It's feasible that something can happen the 513th time text is deleted after the last time the text was saved because of an internal limit - but how many people are going to find this?
Every tester with any experience knows that if they haven't found any bugs, they've missed something. If they've missed something, they don't know how bad it is.
Testing generally focuses on these areas (more or less in this order):

Does the software do what it should do?
Does the software prevent itself doing what it should not do?
Can the software be made to not do something it should do?
Can the software be made to do something it should not do?
Can the software handle unexpected events with grace? (for example, if you pull the network connection mid action will you get a generic error message and no partial transactions or do you get a stack dump and bad data?)
Can the software handle catastrophic events without generating bad data?

A happy tester has gone through to the last of these types of tests, is reasonably confident they have found most of the serious problems, and reasonably confident that none of the bugs they have missed will cause customers to lose valuable data.
I'd add from my experience that testers don't complain about bugs unless they fear that bugs they have found and believe pose a serious risk to the application are not being fixed.
Answer:
Testing Engineer usually force developers to write unit test, must have 80%-90% test coverage. I don't know why 80%-90%?

These numbers are a rule of thumb in the industry. If you would ask "why unit tests at all?" A short answer would be that unit tests force the writer to deeply think about the goal of the production code he will write and, primarily, deeply think about architecture: If you end up with tons of mocking in a unit test, it's signal you have tons of dependencies - which means your code will be fragile to changes in many other places. Unit tests will allow to write the highly-dependable production code and, afterwards, refactor it to remove dependencies. Higher levels of checking do not provide this well because they are not close to the code, but to the abstractions/integrations.

Why they don't write unit test?

I would guess it may fall on at least of the cases:

They read on some book that it's  developer's job;
They do not have the technical skills;
They are 100% filled with other tasks;

The first two cases show that they would need to change their perspective - if their help makes sense in your project, you should talk with them and managers during retrospectives.
The last case would require better understanding of what they are tackling and re-organize yourselves as one single team.
I like to review frontend and backend tests, on every level, to spot missing cases. Migration scripts and boundaries cases in both front and back were specially fragile to missing test cases. Sometimes I am on either one of the last two cases - and I work with the team to change it, because I know the value I can bring to even lower levels of testing - some testers don't...

Should they provide the solution in coding to improve ability to testability or improve quality? and How?

I would not say "provide the solution", but surely they should help both developers and designers to improve testability. Code review is a good tool for this feedback. Writing testable documentation together before writing code or mockups also helps.

They always be happy and then complains about the bugs? However, If the software have no bug, I feel they are unhappy

Well, finding bugs is one of the funniest parts of testing :D
More seriously, not finding bugs (or not having observations) after an exploratory session are signs that maybe the session was not well performed. Software is complex, understanding differs from person to person - and testing is the process of learning about it through exploration and experimentation. So, when a testing session end up with nothing new discovered, it's a sign that we've learned nothing new with the session - which is frustrating.
One ceremony that I've work well to integrate better developers and testers is to use planning time to plan also testing for the following work items. It may help you to talk more about testing in a period where the focus is to understand how the work will be performed. Check out my blog post "A Testing Planning Ceremony for Scrum Teams" for details.
Comment: fyi we recommend reviewing other answers before accepting the first answer.  Even if it is very good, another answer may be a bit better.  Also folsk wishing to help will be disincentivised to help with their knowledge after seeing the quick accept
Comment: Perfect! I like the way you said about Unit Test and Architecture, it opened my mind and change my perspective. Writing Unit Test is no longer boring tasks for me. Thanks for your clear and interesting answer!
Comment: You are welcome. Could you mark the answer as accepted?


Why is I/O uninterruptible?

Question: What is the rationale behind making I/O uninterruptible? What would be the negative consequences if a process handling I/O were allowed to handle a signal?
Comment: `write(2)` is allowed to return early, returning the actual byte count written, which can be less than the buffer length passed as the 3rd arg.
Answer: Any I/O is handled by a system call invoked by a process.  Eventually such a system call will trickle its way down to some appropriate low-level device driver function to perform the actual I/O operation.
I/O can be tricky - to actually get data in and out of the device, various steps may need to be followed, in order and possibly with timing requirements.  If these steps are not completed atomically, the next time they are tried, the device may not respond, misbehave, or even cause the system to lockup.  These steps may be different and unique for each device, hence why there are so many device drivers.
A well written device driver should know how to deal with the device it's trying to service, so it should not normally experience problems unless there's a driver bug, you're using the wrong driver for the device, or the physical device is failing.
Answer: Now that I've read the book "The Design of the Unix Operating Systems" by Maurice Bach, let me answer this question by myself.
In short, making I/O uninterruptible is for the purpose of making the I/O task finish ASAP, without being interfered by signals.
Some related knowledge that I gained from the book:

The word "uninterruptible" should refer to "uninterruptible sleep". When a process is in uninterruptible sleep, it can NOT be woken up by signals, nor can it handle signals.
A process handles signals when: a. it is running in kernel mode and is about to return to the user mode. b. it is about to enter and leave sleep state when the sleep is interruptible.
What happens when a sleeping process is woken up by a signal? It would handle the signal, with the default action being exiting the process. When a process is waiting for I/O completion, you of course do not want it to exit prematurely.
Answer: Some code paths in the kernel are marked uninterruptible, mostly because the code has to comply to strict timing (to answer to a device) or because it is doing something that doesn't admit interference. In Linux' case, most to the former has been pushed out to independent in-kernel treads, and the second ones have been mostly erradicated (I suspect mostly under pressure from the current multi-CPU machines). I.e., it has been some time now that I haven't seen a process in uninterruptible sleep.
Comment: Try reading a scratched CD.
Comment: Or mounting with sshfs and then pulling on the network cord. Uninterrumpible sleep does happen, even nowadays, when underlying media/storage acts up. And it is usually a bloody pain in the arse to deal with.

Why is I/O uninterruptible?