Is it possible that entering and leaving variables are same in simplex method?
Network simplex method, leaving and entering variables
When you are writing Selenium/WebDriver automation scripts you will probably run into the exception NoSuchElementException. You think your selector is working, but somehow the element cannot be found.  What strategy should I take to analyse different reasons that this might be the case?   What should I research and how? Good answers would contain example situations and how to resolve them. (e.g. verify selectors, frames, waiting, etc) How can I take a self-portrait without using a remote?  My camera is a Canon Powershot SX210 IS. I do not have a remote, but I do have a tripod. Given the galois extension $L/K$, where $L=\mathbb{Q}(\zeta, \sqrt[3]{2})$. I've already calculated that $[L:\mathbb{Q}]=6$. I'm trying to prove that the number of intermediate fields is also 6, including $L$ and $\mathbb{Q}$ as intermediate fields. I'm told that the fundamental theorem of galois theory can be useful here, but I can't find a use for it. Sci-fi book, blue critters than only some people can see, kids fight the critters as they feed off energy and are a threat TypeError: 'str' does not support the buffer interface Is there a way to export my artwork as PDF so that it has a transparent background? Something like exporting objects only... whenever I try to save my .ai as pdf, it always comes with a full white background. If I try to save as eps, I get a chunky white background (where it has white rectangles behind the artwork only where the artwork exists, so there are transparent chunks).  If I export as png, I get an image like what I'm looking for. Is there any way to do that in a vector format? Why singularity in a black hole, and not just "very dense"? Why does there have to be a singularity in a black hole, and not just a very dense lump of matter of finite size? If there's any such thing as granularity of space, couldn't the "singularity" be just the smallest possible size? Why does $k/m=\omega^2$ for harmonic motion? Can anyone please give me a proof for $k/m=w^2$ in simple harmonic motion?  I have tried energy conservation and Newton's laws as follows :  In the case of a mass-spring system,  $$F=ma =-kx\\ F=ma = mr\omega^2 $$  hence   $$\frac km  = \omega^2$$  Or   $$\frac12 mv^2 = \frac12kx^2$$  $$\frac km  =  \frac{V^2}{x^2}   =   \omega^2$$  therefore $k/m  =  \omega^2$  Are these valid and correct? I have been stuck in this for the  entire day. What are the downsides of removing ubuntu-desktop metapackage? I once advised someone to remove a package that depends on ubuntu-desktop meta-package, if she didn't need it (EG: if one uses a different editor than gedit). Someone else said that doing so (removing gedit which will in turn remove ubuntu-desktop) could break things. Is this true? Are there any other potential problems? What's an atomic superstate/, and how is it possible?  I understand the basics - being something can be moving and staying still at the same time; the observer changes the behaviour - but I'd like to know a little more, as it interests me, and how is it possible without actually interfering with said thing? As a disclaimer, I must admit this may benefit me (I haven't checked), but probably not as significantly as most others. This issue is also something that has prevented me from answering questions by users with 1 rep in the past, especially if they are poorly fashioned. The Problem New users with a programming question find SO from various methods, such as google. They ask a question with haste, hoping for a quick answer -- which they usually receive. Many of these users have no interest in Stack Overflow itself, but are simply interested in getting the solution they require. As a result of this, they'll check the site regularly for the first day or two until a sufficient answer has been posted. Once they get what they need, they bail; without the required rep or understanding that they should up-vote and select a response as the answer. The Result A great many questions on SO are abandoned by users with no intention of ever coming back. The answer they require has been provided, but for one or more reasons they have neglected their duty of contributing back by way of awarding reputation. The Reach (Since Jeff loves Datum) Some queries on the data dump examine the reach of this 'problem'. The query I used is based on extensions of the following base query; SELECT p1.Id, p1.Score, p1.OwnerUserId, p2.OwnerUserId, p2.Score FROM posts p1  INNER JOIN posts p2 ON (p1.Id=p2.ParentId) LEFT JOIN users ON (p1.OwnerUserId=users.Id) WHERE p2.Score &gt;= 2  AND p2.Score = ( SELECT MAX(p3.Score) FROM posts p3 WHERE p3.ParentId=p1.Id ) AND users.Reputation &lt; 15 AND p1.PostTypeId = 1 AND p1.AcceptedAnswerId = 0  Result: 3,288 Questions by users with under 15 rep which have answers with 2+ up votes that have no accepted answer. Adding: AND (users.LastAccessDate-p1.LastActivityDate) &lt; 604800 // 1 week AND p1.CreationDate &lt; 1249084800 // 1249084800 is 1 week before latest dump data  to the where clause further reveals that 877 questions that have answers with 2+ up votes have no accepted answer, and the owner of the question has not returned since the week the question was asked. Modifying there where clause, and removing the left join: AND p1.OwnerUserId = 0    Reveals a staggering 3,675 questions with answers of 2+ votes by deleted users.  These are questions that were probably answered but the users who did the work can never be recognized. Building off the previous and using an even more restrictive WHERE clause WHERE p2.Score &gt;=5  Still 1,178 posts that can never have an accepted answer. How many posts are there with over 5 up votes that don't provide the correct answer? Modifying the where clause for Reputation to AND users.Reputation = 1  Still reveals 388 questions by users with 1 rep have been abandoned. Solution Similar to how bounty questions work, if a user has abandons the site (not active since x time after the question was asked) with a question that has answers with 2+ up votes, force the answer with the most up votes to be the selected answer. This will reduce the amount of questions that are unanswered, and also give users more of an incentive to answer questions by new users without extra hesitation.  Update Added more statistics for deleted users.  Please feel free to add/remove rules to make this a truly practical feature. How to instantiate polymer component programmatically in dartlang? Carry over long sequence of missing values with Postgres I have a table like this:  create table foo (foo_label text, foo_price int, foo_date date);  insert into foo (           values           ('aaa', 100,  '2017-01-01'),           ('aaa', NULL, '2017-02-01'),           ('aaa', NULL, '2017-03-01'),           ('aaa', NULL, '2017-04-01'),           ('aaa', 140,  '2017-05-01'),           ('aaa', NULL, '2017-06-01'),           ('aaa', 180,  '2017-07-01')         );   As you can see a few values on the foo_price column are missing.  What I need is that missing values get filled up with the "previous" available value in this way:   foo_label | fixed_foo_price | foo_date -----------+-----------------+------------  aaa       | 100             | 2017-01-01  aaa       | 100             | 2017-02-01  aaa       | 100             | 2017-03-01  aaa       | 100             | 2017-04-01  aaa       | 140             | 2017-05-01  aaa       | 140             | 2017-06-01  aaa       | 180             | 2017-07-01   My attempt:  select      foo_label,      (case when foo_price is null then previous_foo_price else foo_price end) as fixed_foo_price,     foo_date from (   select        foo_label,        lag(foo_price) OVER (PARTITION BY foo_label order by foo_date::date) as previous_foo_price,        foo_price,       foo_date       from foo ) T;   As you can see from here:    It doesn't fill completely the '100' series.  Any idea how can I get the wanted result? Someone flagged my question as already answered, but it's not I asked a question regarding a very specific feature of a program and whether or not it works with a larger program.  Within hours someone had marked it with "This question may already have an answer here of a similar question, but not related to my question.  The question I asked IS NOT ADDRESSED in the referred-to question. It's frustrating to spend half an hour putting together an intelligent and specific question, and then have someone mark it as a duplicate (or possible duplicate), which apparently causes people to skip over my question. I haven't received any more responses since the question was flagged.   Two questions:  (1) How do I get this flagging removed and (2) what's the best way to prevent these "helpful" flaggings in the future? Heat production of magnifying glass Why Magnifying glass(convex lens) produces heat when placed in front of sun? As generally acknowledged TeX offers superb formatting capabilities for math in an automated fashion. Nevertheless there are some areas with clear deficiencies  that one either has to accept or manually improve on a case by case basis.  One of the biggies in that respect is TeX's handling of sub-formulas (i.e., material inside a brace group, e.g., and index, but also any group on top-level). TeX sets such sub-formulas always in natural width even if the whole formula is subject to severe stretching or shrinking otherwise. As an example, consider the following (not very sensible) example:  \documentclass{article}  \newlength\x  \begin{document}  \newcommand\formula{$ a+\mathbf{b+c}+d+e+f = \sum_{i=1}^{n-x-y-z} x_{i+j}$}  \settowidth\x{\formula}  \hbox to \x{\formula}    % natural width  \addtolength\x{-20pt}  \hbox to \x{\formula}   % now shrink it a lot  \addtolength\x{100pt}  \hbox to \x{\formula}   % now stretch a lot in the opposite direction  \end{document}   The formula here has a number of obvious sub-formulas in the subscripts and superscript, but for illustration I also added a sub-formula via \mathbf. Of course the usage of \mathbf in this way is wrong!!! (it should not be applied to several symbols), but I'm sure you would find this in documents. In any case just {b+c} would have had the same effect here. Now what do you think happens if we run this?  This:    As one can see the naturally "boxed" sub-formulas are very wrong the moment the rest of the formula is subject to stretching or shrinking.  Until recently no TeX engine successor addressed this issue. With LuaTeX opening up a lot of the internals of TeX I had some hope that this would be different. However, upon studying the manual my conclusion is that this area (sor far it least) has not been addressed (or considered).  As far as I can see the only way something could be done in LuaTeX about this issue would be to  use the mlist_to_hlist callback. However, this would really mean replacing the full math typesetting algorithm, which of course could be a way to solve the problem but ... but what is needed is not that (as 99% of this algorithm is next to perfect) but to add support to not simply box sub-formulas at their natural width.  So long text ... here is the short question:   Is this analysis correct, or did I overlook something? And in case anybody knows: are there plans to look into the sub-formula issue and provide support for it eventually? (it is not listed on the "to-dos" for math)    In case somebody wonders that I talk about "this sub-formula issue" as if it is something like a known thing ... it is, it was already raised way back in  which at the time a some thorough (if not say heated) discussions. Declare a global variable in a Blender session Center of $D_6$ is $\mathbb{Z}_2$ The center of $D_6$ is isomorphic to $\mathbb{Z}_2$.   I have that $$D_6=\left&lt; a,b \mid a^6=b^2=e,\, ba=a^{-1}b\right&gt;$$ $$\Rightarrow D_6=\{e,a,a^2,a^3,a^4,a^5,b,ab,a^2b,a^3b,a^4b,a^5b\}.$$ My method for trying to do this has been just checking elements that could be candidates. I've widdled it down to that the only elements that commute with all of $D_6$ must be $\{e,a^3\}$ but I got there by finding a pair of elements that didn't commute for all other elements and I still haven't even shown that $a^3$ commutes with everything. For example, I have been trying to show now that $$a^3b=ba^3$$ and haven't gotten too far yet but if I had to answer a question like this on the exam, I feel it would be difficult, is there any kind of trick or hints other than brute force using the relations to get that $a^3$ commutes with everything?  For the solution once I have that the center of $D_6$ is what I think then as there is only one group of order $2$ up to isomorphism, it must be isomorphic to $\mathbb{Z}_2$.  Ideally a way that doesn't appeal to $D_6$ as symmetries of the hexagon if that seems possible. Density of Solid States of Compounds One of the wonderful properties of water (as my high school biology teacher would say) is that in its solid form, it is lighter than its liquid form. This means that when temperatures drop below 0 degrees Celsius, the top layer of water on, say, a lake freezes first. This works out pretty well for any fish or other aquatic creatures living underneath, because the lower layers of water will not freeze.  I know that this is an exception to the general rule of solid and liquid states: A given substance, when transformed into its solid state, will generally sink in a container of its liquid state. My question is this: What other substances are exceptions to this rule (if any?). What features do they share with water that are responsible for this? Windows 7 sleeping during operations I've got Windows 7 set up on my media box.  It's set to sleep after 30 mins of inactivity, but it doesn't seem to work as advertised. In the last two weeks it's gone to sleep during a file copy operation and again while encoding an MP4 file.  Is there any way to get Windows to realise that it's actually busy?