Issue with calculating contraction

[cjayross]

For some reason the API has it that

Currently, the left hand side yields the correct value while the right hand side sums the diagonal components of the array representing the tensor literally.

However this is only an issue with contractions on a single tensor (not a product of tensors), and when the contraction yields a scalar. Meaning that the calculation of the Ricci tensor is fine, but the Ricci scalar is not.

[cjayross]

This is an issue with https://github.com/sympy/sympy.

The ~sympy.tensor.tensor.Tensor._extract_data method contracts indices without applying the metric to the arrays in the replacement_dict argument.