Not sure if this is the right place to ask, but all well, I will ask anyway...    I am hard-pressed with finding an online course that teaches General Relativity in full. I would like to learn General Relativity but I cannot seem to find anything on Google. Is there an online course or courses (free or paid, it doesn't matter to me) that someone can recommend or show me? Maybe it's a University that offers it, and I would be fine with that.  Note: I am a beginner to General Relativity.
What are some good books for learning general relativity?
I'm arriving to the US by air, but departing via land. How do I end form I-94 now that it is only electronic? Shift numbers into a different range I was wondering how can I shift my data that fall between a range lets say [0, 125] to another range like [-128, 128].  Thanks for any help Recently I encountered a problem (the first exercise from chapter four of Atiyah &amp; McDonald's Introduction to Commutative Algebra) stating that if $\mathfrak{a}$ is a decomposable ideal of $A$ (a commutative ring with unity), then the prime spectrum of $A/ \mathfrak{a}$ has finitely many irreducible components. This follows easily from the recognition that the maximal irreducible subspaces of $\textrm{ Spec } (A / \mathfrak{a})$ are precisely the "zero loci" of the minimal prime ideals of $A /\mathfrak{a}$.   I'm curious about the converse - the proof isn't easily reversed since the notion of minimal ideals of $\mathfrak{a} $ doesn't make sense before we know what we are trying to prove. My intuition says that it is false based on the general premise that images are badly-behaved (and the fact that it isn't part of the exercise.) However, I've had some difficulty constructing a counterexample, so that the main purpose of this post is to ask for a reasonable procedure or heuristic for doing so (or, of course, proof that my intuition is false.)   If it helps, if $\textrm{Spec }(A / \mathfrak{a})$ is irreducible then the nilradical $\mathcal{R}_{A /\mathfrak{a}}$ is prime so that $r(\mathfrak{a}) = \rho^{-1} ( \mathcal{R}_{A / \mathfrak{a}} ) = \displaystyle\cap_{i=1}^n \rho^{-1} (p_i),$ where $p_i$ are the minimal prime ideals of $A /\mathfrak{a}$ and $\rho $ is the associated projection, is also prime. Thanks! How can we know that all of the results for entangled photons are not chosen when the pair is created? What is the meaning of "build off of"? What is the meaning of "build off of"? I Googled it, but can't find any definition!  I encountered it in the sentence in a technical book. The sentence is:     For the application we will build, the todos example is the closest   fit, so we'll go ahead and build off of that example.   There is a link related to it I found by Google, But it didn't give the definition! Approximating commuting matrices by commuting diagonalizable matrices Suppose the matrices $A$ and $B$ commute. Do there exists sequences $A_n$ and $B_n$ of matrices such that   $A_n \rightarrow A$, $B_n \rightarrow B$.  Each $A_n$ is diagonalizable  and the same for each $B_n$.  For every $n$, $A_n$ commutes with $B_n$.    Moreover, it would be nice if the following property was additionally satisfied: if $A,B$ are real, then $A_n,B_n$ can be chosen to be real as well. When I tried to run , I got the below screen:    The captcha is missing!  I tried in other browsers too.    Update:  From @Oded's comments, I changed to HTTP and it was working perfectly.  Out of curiosity I would like to know why the captcha isn't working when accessing Data Explorer over HTTPS. Import users from CSV file Is it possible to import users by using CSV file? or something like a LDAP connection to import all users? How to read dash files So I paid for a minecraft account and everything but when I try to log in it says that I don't have a username. Is it an email or an email that you've made just for this account? Hat duplicates when info is expanded Why do I get "Permission denied (publickey)" when trying to SSH from local Ubuntu to a Amazon EC2 server? I have an instance of an application running in the cloud on Amazon EC2 instance, and I need to connect it from my local Ubuntu. It works fine on one of local ubuntu and also laptop. I got message "Permission denied (publickey)" when trying to access SSH to EC2 on another local Ubuntu. It's so strange to me.  I'm thinking some sort of problems with security settings on the Amazon EC2 which has limited IPs access to one instance or certificate may need to regenerate.  Does anyone know a solution? Tag scores update is supposed to happen at 03:00 UTC every day. Tag scores are updated by a scheduled job that is time consuming and often times out  (see for example the answers for  and ).  In the past month or two, the issue with not updating the scores has gotten much worse. Tag scores are now regularly not updated for 2-3 days in a row. The job fails more often than it runs which obviously lowers usability and appeal of tag badges (which are not awarded when the script fails) and scores to some extent.  I can also guess that if a job fails on consecutive days, it only makes it harder to make it work as it has more and more tags and answers to recount.  This issue happened in the past but not to the extent it's happening now.  Please do not close it as duplicate. I'm creating a separate post as I've been asked to do it by Adam Lear in a comment for the answer for the first of the linked questions. Other posts reporting this issue have accepted answers which makes them difficult to track for the SE team.  UPDATE  I've been writing down whether the scores were updated or not every day in April.  The results are:  Day      1   2   3   4   5   6   7   8   9   10  11  12  13  14  15   Updated  -   -   -   ✓   -   ✓  -   -   -   -   -   ✓   -   -   -   Day      16  17  18  19  20  21  22  23  24  25  26  27  28  29  30 Updated  ✓   -   ✓   -   ✓   -   -   ✓  ✓   -   ✓  -   ✓   -   -   The update succeeded on 10 days, failed on 20. The situation got somewhat better in the second half of the month. Has something been done about it? How to create a function to sum the required multiple column I have a scenario where i want to sum the multiple column   The data in the file is :  ID|NAME|SAL|COST|PER|TAG  1|A|10|10|20|10|  1|B|10|15|20|10|  1|C|10|17|25|80|  1|D|115|110|20|100|  1|E|10|10|10|10|   i want sum of COLUMN - SAL | COST | PER | TAG   one i did with simple command but how to do by creating function  awk '{FS="|"}{s+=$3}END{print s}' file.txt   The function should be parameterised so that when i pass column name it should calculate sum for that column   The sum column's may differ. their may be requirement like only two column sum needed then it should take the two column names and process the sum for that What did Hisoka do in the Hunter Exam? In the first Hunter Exam of the series (Hisoka's second),  was introduced into the series removing another applicant's arms from his body for bumping into him and not apologizing.    What did he actually do? We know Hisoka's abilities are Bungee Gum and Texture Surprise, but they don't explain how the arms are converting into flower petals as seen above. GZip of drive image created by using `dd` command I created yesterday a drive image using GZip.  I opened the 51.3 GiB file named ssd.img.gz to see one icon thats a package of 3.9 GiB, yes, thats THree point Nine Gigabytes in size and has the name of the image as ssd.img  That does not seem right to me, has the image creation worked or not?  Yes the drives have data and an operating system on it.  Should I have used cat instead? only I did and it kept on saying that it had nothing to do.  Would using the | zip instead be a better option?    ** EDIT **  The command used was:  mark@zotac:~$ sudo -l Enter password:&lt;entered password to get in to root&gt; root@zotac:~# dd if=/dev/sda | gzip -c &gt; "/media/mark/Seagate External Drive/ssd.img.gz   the terminal spent the best part of 10 Hours at building the image, something in itself that I also found suspect, why so log when copying the files to a folder that I wanted, some 40GiB took 45 minutes...  The source drive /dev/sda had no mounted partitions.     ** EDIT **  Just to clarify, I am trying to make an image of the drive to back up later if things go wrong with a repair, the drive itself needs to be a file on a drive as the target drive partition is using almost all of the drive, the partitions can't be resized on it without formatting it and I am not about to lose 1.4TB of data.   So the dd if=/dev/sda of=/&lt;target&gt; isn't what I need, what I do need is an image of the drive that I can restore the image from to the drive should the repair go wrong.  So what command do I use, dd or cat? Why does | zip keep telling me it has nothing to do when used with cat but no error or warning with dd Representation of electromagnetic wave? Is it: My apples and orange are/is wrong? Simple question:     My apples and orange are wrong   or     My apples and orange is wrong   I am not a native English speaker, and I am having some trouble choosing between plural are or singular is for that kind of example. How to initialize a JavaScript Date to a particular time zone I have a file with a number of lines in a file filename.  I want to count how many lines start with character 'a', with 'b' and so on in one go.  What command i should execute.?