Gradient of FE functions
This issue was to discuss if there are already some implementation to evaluate the gradient of an FE function, one related function I could find was evaluateGradient but this is only for 2D and I am not sure if it is tested well also.
For example, if we could evaluate the gradient of a scalar FE function and get the result as a vector FE function. There would be multiple issues to deal with like, what should we do on (faces, ) edges and nodes and how efficiently we perform the evaluation.
I feel this would be useful when we go towards nonlinear rheologies (viscosity) and also maybe for some post-processing in geophysics, like studying the stress field from the velocity field.