How to set a metric tensor inverse?

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I have a complicated metric tensor. In order to compute the Laplacian in this metric, I need the metric tensor inverse. But this exceeds my memory capacity after ~36 hours of computing.

I would like instead to set the inverse with what I believe to be the correct entries. Is that possible? Reviewing the documentation and the source code, I see no indication of such an operation.

I wonder if g.inverse().comp(XI.frame())[:] = Ginv[:] would work, where g denotes the metric tensor, and Ginv the matrix of expressions which should be correct.

BTW, I have the metric and its inverse in one frame. It is after mapping into a second frame [XI] that the problem arises.