I don't have a solution, but a related comment: slicing of large sparse
matrices is very slow too. E.g., I like to assemble a stiffness matrix (for
a PDE) with free boundary conditions and then impose clamped boundaries by
taking a subset of the matrix,
B = A[Ifree, Ifree]
this is so slow that I had to completely give up on it and rewrite all my
assembly codes. I suspect that the flipxx functions and this are a similar issue? Is there already an issue filed for this? Christoph
