Another alternative is to create a shell matrix C with a user context that contains both A and B, then MatMult(C) calls MatMult(A) and MatMultTranspose(C) calls MatMult(B).
> El 25 jun 2020, a las 8:23, Ernesto Prudencio <[email protected]> escribió: > > Thank you, Jose. > > However, in the case of a "matrix free" matrix, the APIs on PETSc seem to > allow just the implementation of A.v, not of A' . w > > One could create another "matrix free" matrix B which could make the role of > computing z = B . w = A' . w. But how could one force the routine > MatMultTranspose(A, w, z) to call the routine for B? Here I am assuming that > MatMultTranspose(A, w, z) is the routine that SLEPc calls internally in its > algorithms when the user sets for implicit transpose. > > I see two possibilities (for brain storming, since I don't know if such > approaches would be acceptable for the PETSc team and/or the SLEPc team): > 1) PETSc could add an entry for a second routine that computes [ A' . w ] > when calling MatMFFDSetFunction() > 2) SLEPc could add an entry for the routine for computing [ A' . w ] when the > matrix A is "matrix free" > > Thanks again, > > Ernesto. > > > Schlumberger-Private > > -----Original Message----- > From: Jose E. Roman [mailto:[email protected]] > Sent: Thursday, June 25, 2020 1:01 AM > To: Ernesto Prudencio <[email protected]> > Cc: [email protected] > Subject: [Ext] Re: [petsc-users] Question on SLEPc + computing SVD with a > "matrix free" matrix > > Yes, you have to set it with SVDSetImplicitTranspose(), but then the > matrix-free matrix should implement both "A.v" and "A'.v" operations. > Jose > > >> El 24 jun 2020, a las 23:25, Ernesto Prudencio via petsc-users >> <[email protected]> escribió: >> >> Hi, >> >> Is it possible to compute a SVD for a “matrix free” matrix? >> >> At first, it seems it would be ok with a MatCreateMFFD() and >> MatMFFDSetFunction(), because one could then provide the routine that >> computes “A . v” for any given v, which is an operation needed by SLEPc. >> However, one would also need to set up the SVD object in SLEPc with an >> implicit transpose. Would that be possible? >> >> Thanks in advance, >> >> Ernesto. >> >> Schlumberger-Private
