Hello everyone, I have a block matrix B and vec x, and need to compute y=Bx many times. I found that each time before I call MatMult(B,x,y,ierr), I need to call VecSet(y,0.0,ierr). Otherwise, the result y is not correct (sometimes, but not always). I have this puzzle even if x and y are created by MatCreateVecs. I am using petsc 3.7.6 fortran api.
If I create the same B in non-block format, it works fine without the extra vecset. It seems that I cannot reuse the allocation of vec y for block matrix without a reset. Is there any clue to explain this behavior? Thank you. Best, Xiangdong
