You are correct. That's essentially what I'm doing ATM. That particular step has never been a bottle-neck in any of my Matlab code. Doing things in place in nice when you can, but I'm not going to ruminate over it too much.
On Wednesday, February 12, 2014 4:45:36 PM UTC-5, Steven G. Johnson wrote: > > > > On Wednesday, February 12, 2014 3:41:21 PM UTC-5, Jason Pries wrote: >> >> FWIW, The place I use this the most is when solving PDEs using finite >> elements with Dirichlet/Periodic boundary conditions. If I want to preserve >> the symmetry of the matrix before factorization, I end up needing to delete >> some rows and columns. I could write the code to create the matrix the way >> I end up using it, but that would require every function that creates a >> matrix to know about the boundary conditions which complicates things >> considerably. >>> >>> >>> > Note that you can do this out-of-place via B = A(I,J), where I and J are > arrays of the desired indices. The question is how important is in-place > operation here; for sparse matrices, the matrix storage is usually small > compared to that of the factorization (for sparse-direct solvers). >
