RicciSign in RiemannToWeyl and WeylToRiemann

[Leslaw Rachwal]

Hello everyone,

I met the following issue in using automatic functions in the xTensor package. Even if I set explicitly the variable $RicciSign to -1 there is no change in the result of functions RiemannToWeyl and WeylToRiemann transforming the respective tensorial expressions, compared to the default case $RicciSign=+1. I looked into the code of these functions and surprisingly there I do see dependence on $RicciSign, which is included in the code correctly. I guess there may be something wrong with further processing of Ricci tensor and Ricci scalar which cancels this dependence on the sign. For the moment I  easily wrote the functions which depend on the sign by myself and they work but I would like to understand (and maybe also contribute to solving) what is the source of this problem in xTensor. Thanks for your attention.

Best,

Leslaw

[Jose]

Hi,

These signs are global variables, and should be consistent throughout a given xAct session. In other words, they should be set at the beginning of the session, before using any of the Def commands. A command like DefMetric will create static structures and relations hardwiring the values that some of these signs had at that time.

In your particular case, set $RicciSign = -1 **before** calling DefMetric. If you want to see what DefMetric stored internally, check the result of

?xAct`xTensor`Private`RiemannToWeylRules

Cheers,

Jose.

[Leslaw Rachwal]

Dear Jose,

Thanks for your advice. Of course, it works when I put $RicciSign=-1 before DefMetric. This solves my issue. Once again thanks a lot.

Best regards,

Leslaw Rachwal