How can I center the following boxes using CSS I am trying to center the boxes horizontally. Currently they are aligned to the left and when you resize the window they move responsively. I would still like to keep that functionality. I just want to center the boxes even when I resize the window. I tried float:center but there is no such thing...Thank you.    .mybtn { font:bold 20px"Arial Black", Gadget, sans-serif; font-style:normal; color:#ffd324;  background-color: rgba(255,0,0,.90); border:2px solid #000; text-shadow:0px -1px 1px #222222; box-shadow:0px 0px 12px #2e2300; -moz-box-shadow:0px 0px 12px #2e2300; -webkit-box-shadow:0px 0px 12px #2e2300; border-radius:15px 15px 15px 15px; -moz-border-radius:15px 15px 15px 15px; -webkit-border-radius:15px 15px 15px 15px; width:100px; height:100px; margin:5px; float:left; position:relative; }   And the HTML  &lt;div class="mybtn"&gt;  &lt;/div&gt;  &lt;div class="mybtn"&gt;  &lt;/div&gt;  &lt;div class="mybtn"&gt;  &lt;/div&gt;  &lt;div class="mybtn"&gt;  &lt;/div&gt;  &lt;div class="mybtn"&gt;  &lt;/div&gt;
How to horizontally center an element How can I horizontally center a &lt;div&gt; within another &lt;div&gt; using CSS? &lt;div id=&quot;outer&quot;&gt;   &lt;div id=&quot;inner&quot;&gt;Foo foo&lt;/div&gt; &lt;/div&gt;
I observed some naive examples. Spheres, for example, when we cut out one point, can be embedded into $\mathbb{R}^n$. And if we cut out a measure zero set of a projective space, it can be embedded into the Euclidean space of the same dimension. So I wonder if all manifolds can be embedded into a same dimensional Euclidean space when we cut out a measure zero set? Can anyone prove it or disprove it by giving me some counterexamples? I am looking for a textbook that treats the subject of Special Relativity from a geometric point of view, i.e. a textbook that introduces the theory right from the start in terms of 4-vectors and Minkowski tensors, instead of the more traditional "beginners" approach. Would anyone have a recommendation for such a textbook ?  I already have decent knowledge of the physics and maths of both SR and GR ( including vector and tensor calculus ), but would like to take a step back and expand and broaden my intuition of the geometry underlying SR, as described by 4-vectors and tensors. What I do not need is another "and here is the formula for time dilation..." type of text, of which there are thousands out there, but something much more geometric and in-depth.  Thanks in advance. Does a photon exert a gravitational pull? I know a photon has zero rest mass, but it does have plenty of energy. Since energy and mass are equivalent does this mean that a photon (or more practically, a light beam) exerts a gravitational pull on other objects? If so, does it depend on the frequency of the photon? Is there a quick way to set an HTML text input (&lt;input type=text /&gt;) to only allow numeric keystrokes (plus '.')? As linguistics student, I have to put more than one thing on a character every now and then. For example, I need to type ā̆. I thought I could simply do that by typing \={\u{a}}, but then the macron is placed above an empty space in front of the character.  How can I solve this? Thanks  P.S. I'm using MiKTeX 2.9, running on Windows 8; in case it might be of use. Increasing extent of Raster? EntityFieldQuery order by title Based on newtons third law If an elephant can apply 250N force and a rabbit can apply 25N force , and if they are pulling each other , then elephant will pull with 250N force and according to newtons third law the rabbit should also pull the elephant with 250N force.then from where do the rabbit got the extra 225N i.e.(250-25=225) force??? can anyone please explain. How to get an enum value from a string value in Java? Say I have an enum which is just public enum Blah {     A, B, C, D }  and I would like to find the enum value of a string, for example &quot;A&quot; which would be Blah.A. How would it be possible to do this? Is the  the method I need? If so, how would I use this? Where did Schrödinger solve the radiating problem of Bohr's model? One of the problems with Bohr's theory to describe the hydrogen atom, was that the electron orbiting around the nucleus has an acceleration. Therefore it radiates and loses energy, until it would collapse with the nucleus.  Now Schrödinger describes the electron as a wave function. His theory is able to describe all atoms (in contrast to Bohr's model), but how is the radiation problem solved? I understand that the wave has not an exact position in the time anymore. But the electron still "moves", so it has an acceleration anyway (because of vibrations or so).   Why is in this theory the electron not radiating anymore? And if it is, why doesn't the atom collapse? Placing a single algorithm in two columns I was wondering if someone could critique my argument here. The problem is to find the probability where exactly 2 people in a room full of 23 people share the same birthday.  My argument is that there are 23 choose 2 ways times $\displaystyle \frac{1}{365^{2}}$ for 2 people to share the same birthday. But, we also have to consider the case involving 21 people who don't share the same birthday. This is just 365 permute 21 times $\displaystyle \frac{1}{365^{21}}$. To summarize:  $$\binom{23}{2} \frac{1}{365^2} \frac{1}{365^{21}} P\binom{365}{21}$$ How to squeeze error message out of PDO? A book in which every species on earth was rendered intelligent The 'blurb' on the back of the book was that something had boosted the intelligence of every creature on earth, to the point that at least some animals were on par with humans. I'm not sure if humans were similarly enhanced or just animals. I'm not sure whether it was done by aliens, or a side effect of something humans did, or what.   This book was on the shelves in the mid/late 1980's, so it's nothing more recent than that. I am trying to create a beamer animation using tikz, but I can't even get basic rotating of a tikz image working as desired.  I have a rectangle specified by  \draw[rounded corners,dotted] (-3.5,0) rectangle (-0.5,2);   I would like to rotate this rectangle about the point (-1,.5) (which is near the bottom right corner of the rectangle).  I've tried:  {\rotatebox[origin=c,x=-1,y=.5]{130}{             \draw[rounded corners,dotted] (-3.5,0) rectangle (-0.5,2);}}   But this produces an error.  If I just use the origin=c option, it compiles, but it rotates the rectangle about the point (0,0).  I've also tried it with just the x=-1,y=.5 (without the origin option), and it fails to compile.  I have searched the documentation, which is where I learned about the options x=xdim and y=ydim.  However, I can't find a single example demonstrating how these options should be used.  Any suggestions would be greatly appreciated.    Also, if there is a better command for rotating things that will be more suitable for use in a beamer animation, please let me know.  Thanks! Clustering on the output of t-SNE I've got an application where it'd be handy to cluster a noisy dataset before looking for subgroup effects within the clusters.  I first looked at PCA, but it takes ~30 components to get to 90% of the variability, so clustering on just a couple of PC's will throw away a lot of information.    I then tried t-SNE (for the first time), which gives me an odd shape in two dimensions that is very amenable to clustering via k-means.  What's more, running a random forest on the data with the cluster assignment as the outcome shows that the clusters have a fairly sensible interpretation given the context of the problem, in terms of the variables that make up the raw data.  But if I'm going to report on these clusters, how do I describe them?  K-means clusters on principal components reveal individuals who are nearby to one another in terms of the derived variables that comprise X% of the variance in the dataset.  What equivalent statement can be made about t-SNE clusters?  Perhaps something to the effect of:     t-SNE reveals approximate contiguity in an underlying high-dimensional manifold, so clusters on the low-dimensional representation of the high-dimensional space maximize the "likelihood" that contiguous individuals will not be in the same cluster   Can anyone propose a better blurb than that? I get double question marks when referring to labels inside figures I have some charts embedded in figures, and I want to be able to refer to them easily using the "Figure x" notation. I'm doing it like this (in this order):  \documentclass[12pt,letterpaper]{article}  ...  \section*{Results} ...we performed a linear regression to obtain a standard curve  (Figure~\ref{0:stdcurve})....  \pagebreak \section*{Results (Graphs)} \subsection*{Construction of Standard Graph for PNP} \begin{figure}[h]   % Figure 1     \centering     \includegraphics[scale=1]{kinematics-res/graph0-1}     \caption{The standard curve for PNP.}     \label{0:stdcurve} \end{figure}   However, instead of getting the output "...to obtain a standard curve (Figure 1)...", I just get "...to obtain a standard curve (Figure ??)..."  I also noticed that the PDFLaTeX compiler is generating warnings saying that it couldn't find the reference of the name 0:stdcurve. Why am I getting these warnings? Allow retracting a moderator flag if the post has been deleted and I don't have enough reputation to see deleted posts Currently, custom flags for moderator attention are not automatically invalidated (marked helpful) when a post gets deleted. Ordinarily, one can retract a moderator flag by going to the post, clicking &quot;flag&quot;, and then &quot;Retract Flag&quot;. This works even if the post has been deleted, provided they can see the post (they have 10,000+ rep, it's their own post, or they have answered it). However, it's not possible to self-remove a flag on a deleted post if they can't see the deleted post, because they can't get to the &quot;flag&quot; button. Is this intended? If not, can this ability please be implemented? As Aurora0001 commented, there is no server-side check, the button is just not visible. Can this please be implemented on the website, or is the fact that it's possible server-side a bug that will soon be fixed by removing it? Are there massless bosons at scales above electroweak scale? Spontaneous electroweak symmetry breaking (i.e. $SU(2)\times U(1)\to U(1)_{em}$ ) is at scale about 100 Gev. So, for , gauge bosons $Z$ &amp; $W$ have masses about 100 GeV. But before this spontaneous symmetry breaking ( i.e. Energy > 100 GeV) the symmetry $SU(2)\times U(1)$ is not broken, and therefore gauge bosons are massless.  The same thing happens when we go around energy about $10^{16}$ GeV, where we have the Grand Unification between electroweak and strong interactions, in some bigger group ($SU(5)$, $SO(10)$ or others). So theoretically we should find gauge bosons $X$ and $Y$ with masses about $10^{16}$ GeV after GUT symmetry breaks into the Standard Model gauge group $SU(3)\times SU(2)\times U(1)$, and we should find massless X and Y bosons at bigger energies (where GUT isn't broken).  So this is what happened in the early universe: when temperature decreased, spontaneous symmetry breaking happened and firstly $X$ &amp; $Y$ gauge bosons obtained mass and finally $Z$ &amp; $W$ bosons obtained mass.   Now, I ask: have I understood this correctly? In other words, if we make experiments at energy above the electroweak scale (100 GeV) we are where $SU(2)\times U(1)$ isn't broken and then we should (experimentally) find $SU(2)$ and $U(1)$ massless gauge bosons, i.e. $W^1$, $W^2$, $W^3$ and $B$ with zero mass? But this is strange, because if I remember well in LHC we have just make experiments at energy about 1 TeV, but we haven't discovered any massless gauge bosons. Which is correct if I want to request for a pen?        Can I have your pen please?   May I have your pen please?