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I do not understand why the output of the two commands:

metric[-c, -d] (CD[d][RicciScalar[CD][]]) (CD[c][RicciScalar[CD][]]) // Simplify,

(CD[-c][RicciScalar[CD][]]) (CD[c][RicciScalar[CD][]]) // Simplify,

is different. The first one outputs a scalar function, as expected, whereas the second gives an expression

enter image description here

that I do not know how to contract.

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    $\begingroup$ Can you provide a minimal version of your code that reproduces the error when run on a "clean" kernel? It may help in tracking down the problem. $\endgroup$
    – Michael Seifert
    Oct 8, 2021 at 19:47

1 Answer 1

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You have a product of a Basis[-c, {1, B}], for some basis B, and a CTensor[comps, {B}][c] object.

You can use ContractBasis to force the contraction of a Basis[...] object with anything.

Or you can use FromBasisExpand to convert a Basis[...] object into a CTensor object, and the two CTensor objects will then be automatically contracted.

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