Problem with Solve conventions

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Andrew

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Mar 7, 2023, 9:15:01 AM3/7/23
to xAct Tensor Computer Algebra
Hi

I have just installed Mathematica 13 and xAct 1.2.0 on my new machine and I've encountered a problem when using one of my old notebooks.

In the attatched notebook on the final output we see that the the convention for Solve[] acting on xAct quantities is not consistent which messes up many of my old notebooks.

Should I install an old version of Mathematica or can the new version be patched to avoid this issue?

Many thanks
Andrew
Solve-problem.nb

Thomas Bäckdahl

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Mar 9, 2023, 11:29:29 AM3/9/23
to xa...@googlegroups.com

Hi!

This seems a bit annoying.

Unfortunately Solve can do some random choices. To be sure that you are solving for the variables you intended, you could do something like

Quiet@Solve[AllWeyls, Cases[AllWeyls, WeylCD[__], Infinity]]

Then it will only try to solve for the variables of the form WeylCD[__]. 
Unfortunately you can not use the pattern directly in Solve, so you need to extract the versions you have with Cases[AllWeyls, WeylCD[__], Infinity]. If you want preference to some variables, you can sort this list in some way.
Quiet is there to suppress a message about impossibility of solving for all of the listed variables.

I think that this method should be more stable under changes of versions of Mathematica.

Regards
Thomas

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