Enforce contraction on a particular tensor while UseMetricOnVBundle -> None ?

[BN]

Hello,

I am new to xAct and still learning, the package is really amazing. I am probably being too picky, but here is what I would like to do:

I am handling some big expressions, and among other tensors there appears Weyl tensor.

In the expressions manipulation I use ToCanonical with UseMetricOnVBundle -> None because I do not want to perform contractions on all terms/objects. But at some point I need to perform contraction only on the Weyl tensor so that I would make terms proportional to its trace vanish, while the rest of the terms are untouched by any raising/lowering/contractions. So my question is:

Is there are a way to enforce the use of the index contraction on a specific tensor only, bypassing the option UseMetricOnVBundle -> None  only for that tensor? Alternatively, is there a way to prevent a tensor from being affected by contractions during the use of ToCanonical with UseMetricOnVBundle -> All ?

Regards,

Branislav

[Jose]

Hi,

For a given vbundle, ToCanonical cannot move slots/indices of only some tensors. Either it can move them up and down for all tensors on that vbundle, or none. The property of a slot being "movable" needs to be propagated by symmetry. The property of a pair {a, -a} being "exchangeable" needs to apply to all pairs or none.

You can try to construct rules that apply ContractMetric only with some tensors, before using ToCanonical with UseMetricOnVBundle -> None, but I cannot guarantee this will work self-consistently.

Cheers,

Jose.