Ingo Gaertner <[email protected]> writes: > Does PETSc include an efficient implementation for the operation > y=(A-diag(A))x or y_i=\sum_{j!=i}A_{ij}x_j on a sparse matrix A? > > In words, I need a matrix-vector product after the matrix diagonal has been > set to zero. For efficiency reasons I can't copy and modify the matrix or > first calculate the full product and then subtract the diagonal > contribution.
How many entries per row in your matrix? There isn't a special function for this, but I'm skeptical that the performance gains of a custom implementation would be significant. Do you have a profile showing that it is?
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