Dear firedrakers, can I somehow check whether a dat/function has been written to since I last performed a given operation on it? I have a banded matrix A stored in each cell on mesh, and whenever I solve the equation A.x = b (separately in each column, of course) I want to do this in two steps: (1) calculate the LU decomposition (lapack dgbtrf) (2) solve based on that LU decomposition (lapack dgbtrs) I have to do a lot of solves, so for efficiency I want to only do (1) if my matrix A has changed. So when I do a solve, I check if a flag lu_decomp is True (and this flag is set to False upon matrix creation). If it is, then I go straight to (2), otherwise I do (1) first. But I need to make sure that whenever my banded matrix has been written to lu_decomp is set back to False. Thanks, Eike