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Why can I no longer easily navigate inside of this mesh? How to pad zeroes to a string? How to prove that a limit does not exist? Let $x \in \mathbb{R}$ and let $\lfloor y\rfloor$ be the largest integer less than or equal to $x$. $$ f(x) = \frac{1}{x} - \left\lfloor\frac{1}{x}\right\rfloor$$ How does one prove that the $ \lim_{x\to 0} f(x)$ does not exist by using a Epsilon Delta proof? There is a hint given that you can use a proof by contradiction. Finding an angle within an 80-80-20 isosceles triangle du shows completely different folder size for * and folder name I'm trying to move some data over and to start with I'd like to make sure that the size is ok. I run into a problem however, if I check the folder with   du -sh  myfolder/ 780M    myfolder/   but   du -sh * .. 71M     myfolder ..   I thought it might be something to do with hidden files but this particular folder does not have any inside.  Am I missing something? Time-Stream Crossing and Forgetfulness In The Day of the Doctor, it's explained that the Doctor doesn't remember having interacted with himself, and if he interacts with a future version of himself, the younger version forgets.  But in Time Crash, 10th solves the problem of the TARDISes occupying the same space because he remembers himself doing it from when he was 5th.  If this is true, 5th wouldn't have wondered whether or not he was going to regenerate when he did.  Does the TARDIS occupying the same space with itself re-instate those memories? Or is it just possible that I'm asking a ridiculous question that will never have an answer because Doctor Who.  :D An "urgent" tag for questions that need answers within minutes When no model comparison, should I use REML vs ML? I'm running LMM, and I will make no comparison of models. Could I ask which one should I use between REML and ML? SVG for images in browsers with PNG fallback Setting-up SSH-tunnel for VPN? In the  question one of the answers had the following code snippet:  IEnumerable&lt;object&gt; FilteredList() {     foreach(object item in FullList)     {         if(IsItemInPartialList(item))             yield return item;     } }   What does the yield keyword do there?  I've seen it referenced in a couple places, and one other question, but I haven't quite figured out what it actually does.  I'm used to thinking of yield in the sense of one thread yielding to another, but that doesn't seem relevant here. I asked about it on  and they told me to post it here.  Probably need to add the :active to the :hover meta class or something like that.  Example:      Hammer Time I have a set of polygons representing administrative districts.  The districts were digitized by hand, and there are small spaces (slivers) between polygons where the polygons should be touching. How can I have the polygons snap together, removing the spaces? How should I interpret this residual plot? I am unable to interpret this graph. My dependent variable is total number of movie tickets that will be sold for a show. The independent variables are the number of days left before the show, seasonality dummy variables (day of week, month of year, holiday), price, tickets sold till date, movie rating, movie type (thriller, comedy, etc., as dummies). Also, please note that movie hall's capacity is fixed. That is, it can host maximum of x number of people only. I am creating a linear regression solution and it's not fitting my test data. So I thought of starting with regression diagnostics. The data are from a single movie hall for which I want to predict demand.  The is a multivariate dataset. For every date, there are 90 duplicate rows, representing days before the show. So, for 1 Jan 2016 there are 90 records. There is a 'lead_time' variable which gives me number of days before the show. So for 1 Jan 2016, if lead_time has value 5, it means it will have tickets sold until 5 days before the show date. In the dependent variable, total tickets sold, I will have the same value 90 times.  Also, as a side remark, is there any book that explains how to interpret residual plot and improve model afterwards? What canonical momenta are the "right" ones? I'm doing some classical field theory exercises with the Lagrangian $$\mathscr{L} = -\frac{1}{4}F_{\mu \nu}F^{\mu \nu}$$ where $F_{\mu \nu} = \partial_\mu A_\nu - \partial_\nu A_\mu$. To find the conjugate momenta $\pi^\mu_{\ \ \ \nu} = \partial \mathscr{L} / \partial(\partial_\mu A^\nu)$, I can use two methods.  First method: directly apply this to $\mathscr{L}$. We get a a factor of $2$ since there are two $F$'s, and another factor of $2$ since each $F$ contains two $\partial_\mu A_\nu$ terms, giving $$\pi^\mu_{\ \ \ \nu} = -F^\mu_{\ \ \ \nu}.$$  Second method: get $\mathscr{L}$ in terms of $A$ by expanding and integrating by parts, yielding $$\mathscr{L} = \frac{1}{2}(\partial_\mu A^\mu)^2 - \frac{1}{2}(\partial_\mu A^\nu)^2.$$ Differentiating this gets factors of $2$ and gives $$\pi^\mu_{\ \ \ \nu} = \partial_\rho A^\rho \delta^\mu_\nu - \partial^\mu A_\nu.$$  These two answers are different! (They do give the same equations of motion, at least.) I guess that means doing the integration by parts changed the canonical momenta.  Is this something I should be worried about? In particular, I have another exercise that wants me to show that one of the canonical momenta vanishes -- this isn't true for the ones I get from the second method! Plus, my stress-energy tensor is changed too. When a problem asks for "the" canonical momenta, am I forbidden from integrating by parts? Map display not filling window in QGIS on Mac? How do you evaluate this integral $\int \frac{6x^{3}+7x^2-12x+1}{\sqrt{x^2+4x+6}}dx$ $$\int \frac{6x^{3}+7x^2-12x+1}{\sqrt{x^2+4x+6}}dx$$  I have met this complex integral today, how do you evaluate this? Can you do this in more steps?  Is this an elliptic integral? I don't know how to evaluate this integral at all. Automatic pyqgis categorized renderer classification I have some layers in my project and I would like to alter their styles, since ranges of values for underlying columns have changed.  Normally it would require to enter each layer style settings separately and trigger "Remove All", and "Classify" button, however I would like to execute it from the code.   I found such method for graduated symbol:  renderer.updateClasses(layer,0,bins)   ,however I'm having trouble to find corresponding method for categorized symbol class  Is there any way to do this from pyqgis without the need to specify the layer style from the scratch (create category, label etc.) ? Some equivalent of "Classify" button from below screenshot: This book came out of the 1970s (early 1980's) at the latest. In it the protagonist, a not so diligent student, gets turned on to computer programming and creates (I think..) a weather program.   Eventually he moves on and years later the program contacts him. It has become an AI and he is its creator.  I forget what the setup is post contact which is not helpful at all.. bash variables in for loop range I want to print list of numbers from 1 to 100 and I use a for loop like the following:  number=100 for num in {1..$number} do   echo $num done   When I execute the command it only prints {1..100} and not the list of number from 1 to 100.