Thanks. If this is the case, will the option MAT_IGNORE_ZERO_ENTRIES be helpful?
Xiangdong On Thu, Dec 1, 2011 at 8:00 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > On Dec 1, 2011, at 6:44 PM, Xiangdong Liang wrote: > >> Hello everyone, >> >> I have a question about whether zeros will change the sparse pattern. >> Suppose I am generating two sparse matrices A and B. A is generated >> with exactly number of nonzeros, say 10 nnz per row. When I generate >> matrix B, I specify 12 nonzeros, but two of them are given zero values >> by MatSetValue. Will A and B have same sparsity patterns and >> performance ? In other words, will PETSc simply ignore these zeros >> entries? ?I output these A and B in matlab, and it seems that these >> zeros entries are ignored. I just want to double check on this. >> >> Is the option MAT_IGNORE_ZERO_ENTRIES on by default? > > ? No, by default PETSc will insert the zero values thus increasing the > nonzero pattern. If you set that option to the matrix then inserting values > it will not introduce an increase in the pattern. > > > ? ?BTW: if you then load the matrix via a binary file to MATLAB it may be > that MATLAB silently removes those locations so you don't see them. > ? Barry > >> Thanks. >> >> Best, >> Xiangdong > >
