20191012 08:35:52 0500  commented question  jmol stuck at "Initializing 3D display" For the record, the issue is fixed in SageMath 8.9, thanks to the update of Jmol performed in #25026. 
20191010 16:26:48 0500  answered a question  Inverse of the transition map on a Manifold doesn't hold As said at the end of the message, a failed report can reflect a lack of simplification and not a true failure. This is the case here, because on the intersection domain D, z < 0 and w > 0, so you can conclude that It is a pity though that Sage does not arrive automatically at the same conclusion. This is a weakness of the current simplifying mechanism on subcharts and should be improved in the future. 
20191007 03:24:56 0500  commented answer  sage8.9 fails compilation in Ubuntu 18.04 @dsejas Yes indeed the Ubuntu package 
20191005 15:45:12 0500  commented answer  Changing chart multiple times in sagemanifolds SageMath 8.9 is out now. You can check that your example works nicely with it. 
20191004 10:34:09 0500  commented answer  sage8.9 fails compilation in Ubuntu 18.04 I've just compiled successfully Sage 8.9 (Python 3 version) from scratch on a Ubuntu 18.04 computer. The only pngrelated package installed on that computer is 
20191001 00:59:41 0500  answered a question  sage8.9 fails compilation in Ubuntu 18.04 On Ubuntu 18.04, you should install the Ubuntu package 
20190930 08:16:16 0500  commented answer  Transformation of derivative under a change of chart I am not sure to understand what you want exactly. The $\mathrm{D}_0\Phi$ notation gets rid of expressions like $\partial/\partial(r\sin\theta)$. I agree that the Pynac notation $\mathrm{D}_0\Phi$ is not standard mathematical notation and that $\partial\Phi/\partial x$ would be preferable here. I am afraid there is no simple way to achieve this in SageMath, since symbolic functions, as defined with 
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20190929 03:46:01 0500  answered a question  Interactive linear programming According to the documentation returned by your input code is not correct, since 
20190927 15:41:00 0500  answered a question  Transformation of derivative under a change of chart You can use Then $\mathrm{D}_0 \Phi$ stands for $\frac{\partial \Phi}{\partial x}$, etc. See here for details about the display options. 
20190927 05:02:40 0500  answered a question  Display connection coefficients under a change of chart The issue arises because the transition map from chart Then the display of the connection coefficients w.r.t. (*) while investing your issue, I've discovered that the computation can be significantly improved by reordering some loops; this is now Trac #28543. 
20190925 15:02:41 0500  commented question  Stack overflow in boolean test Confirmed with Sage 8.9.rc0, as well as with Sage 8.3. So the bug has been there for a while... 
20190925 14:01:17 0500  answered a question  Saving notebooks with 3dplots In the Jupyter notebook:

20190925 06:38:56 0500  commented question  Interaction with a graphics You can use Equivalently, you can use a double backslash: 
20190912 16:28:08 0500  commented answer  jmol stuck at "Initializing 3D display" This bug is another motivation for #22408. @Emmanuel_Charpentier: which "own share of problems" has 
20190912 16:25:28 0500  commented answer  jmol stuck at "Initializing 3D display" Another workaround is to run the code in a Jupyter notebook. There it is the JavaScript version of Jmol that is invoked, note the Java one, and it works (tested with Ubuntu 18.04). 
20190912 16:22:46 0500  commented question  jmol stuck at "Initializing 3D display" Same issue with Ubuntu 18.04 (OpenJDK 11.0.4). 
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20190908 14:52:19 0500  answered a question  simplify not working correctly with conjugate? Well, it seems that when using (I am a little bit puzzled by this, since I thought Sage's symbolic variables are assumed complex by default) But and So, regarding your example, you have to use 
20190908 08:49:42 0500  answered a question  Error computing curvature of graph submanifold Thanks for reporting this issue. This is a bug, which is now fixed in the ticket #28462. Hopefully, this ticket will be merged in Sage 8.9 (to come out soon). With #28462, your code leads to Side note: your declaration of As you can see, the output is illformed, because The correct declaration should be which leads to Forturnately, EDIT (14 Sep. 2019): the fix introduced in #28462 has been merged in Sage 8.9.rc0, so the next stable release of Sage will be free from this bug. 
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20190830 04:24:58 0500  commented answer  Changing chart multiple times in sagemanifolds @my_screen_name: you are right: in the current stable version of Sage (8.8), there are unnecessary restrictions in the handling of coordinate changes. This is fixed by the Trac ticket #28072, which has been merged in Sage 8.9.beta2. In particular, with run with Sage 8.9.beta8, your original code gives no error and displays $g = \mathrm{d}z\otimes\mathrm{d}z$ in the last line. I have edited my answer accordingly. 
20190829 14:37:08 0500  answered a question  Changing chart multiple times in sagemanifolds The issue arises because you have not fully defined the transition maps on the manifold: the inverse maps are missing. You have to generate them by invoking just after the definition of just after the definition of The reason why the inverse transition maps are not automatically evaluated is that in certain cases Sage is not capable to compute them (the method EDIT: actually, in the present case, the inverse transition maps should not be required to compute the expression of $g$ in the third frame. This will be fixed in the next release of SageMath, thanks to the Trac ticket #28072, which has been merged in SageMath 8.9.beta2. 
20190828 06:24:23 0500  answered a question  How to set a metric tensor inverse?
Probably we should implement a method 
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20190822 15:18:04 0500  answered a question  Setting the components of a differential form systematically. You should write Indeed, when Side note: in your example, the line is useless, because the elements of the dictionary If you want to give names to the differential forms Then 
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20190814 09:51:40 0500  answered a question  Source for Principal Null Directions Kerr, Example Worksheet The vectors $\ell$ and $k$ introduced in this notebook correspond to Eqs. (12.3.5) and (12.3.6) of Wald's textbook General Relativity (1984). You can check that they do define repeated principal null directions, i.e. that they obey the following identity (where $C^a_{\ \ bcd}$ stands for the Weyl tensor) $$ C^a_{\ \ mn[b} k_{c]} k^m k^n = 0,\qquad\qquad\mbox{(1)}$$ with SageMath itself (no need of Mathematica ;)). It suffices to run (same notations as in the original notebook) which yields If you prefer to use index notations (passed as strings in LaTeX format) instead of the outcome of which is A Jupyter notebook implementing the check of (1) by both methods is posted here. 
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20190627 08:08:41 0500  answered a question  (Update) How to change/set variables? Once, 
20190623 10:54:57 0500  answered a question  Tensor ordering Yes this is the second form, namely $$ S^{abc}_{\quad def} T^{ghi}_{\quad jbk} = R^{acghi}_{\quad \ \ defjk} $$ This is so because in SageMath, the contravariant indices come always before the covariant ones. 
20190620 10:18:12 0500  edited answer  Opening "old" Sage Notebooks in Jupyter: not UTF8 encoded You cannot open your Under "Convert old notebooks to Jupyter", you will see the list of your 