I'm a beginner with PETSc, so please forgive me if this is obvious, but I couldn't seem to find any help in the archives.
I'm trying to just the hang of the software, so I've been messing around with routines. I'm going to need complex matrices (Maxwell's with PML) so everything is configured for this. I'm messing around with some very simple test cases, and have a symmetric (but not Hermitian) complex matrix with 2-2i on the diagonal and -1+i on the upper and lower diagonals. I am reading this in from a petsc binary file (again, for testing purposes, eventually I'm going to be just reading in my matrix and RHS). I view the matrix, and it has been read in correctly. I perform LU factorization by doing the following (where ISCreateStride(PETSC_COMM_WORLD,m,0,1,&perm); has been called earlier): MatConvert(A,MATSAME,MAT_INITIAL_MATRIX,&LU); MatFactorInfoInitialize(&luinfo); MatLUFactor(LU,perm,perm,&luinfo); I get that LU is: (1,1) 0.2500 + 0.2500i (2,1) -0.5000 (1,2) -1.0000 + 1.0000i (2,2) 0.3333 + 0.3333i (3,2) -0.6667 (2,3) -1.0000 + 1.0000i (3,3) 0.3750 + 0.3750i (4,3) -0.7500 (3,4) -1.0000 + 1.0000i (4,4) 0.4000 + 0.4000i (5,4) -0.8000 (4,5) -1.0000 + 1.0000i (5,5) 0.4167 + 0.4167i (6,5) -0.8333 (5,6) -1.0000 + 1.0000i (6,6) 0.4286 + 0.4286i Now, I am interpreting this as L being unit on the diagonal and the lower diagonal portion of this "LU" matrix, while U being the diagona + upper of this "LU" matrix. I can interpret this the other way around as well, and it doesn't matter. However, knowing the LU factorization, it is VERY clear the the proper LU decomposition would have the inverse of the diagonal elements presented here. So I believe I should have LU as: (1,1) 2.0000 - 2.0000i (2,1) -0.5000 (1,2) -1.0000 + 1.0000i (2,2) 1.5000 - 1.5000i (3,2) -0.6667 (2,3) -1.0000 + 1.0000i (3,3) 1.3333 - 1.3333i (4,3) -0.7500 (3,4) -1.0000 + 1.0000i (4,4) 1.2500 - 1.2500i (5,4) -0.8000 (4,5) -1.0000 + 1.0000i (5,5) 1.2000 - 1.2000i (6,5) -0.8333 (5,6) -1.0000 + 1.0000i (6,6) 1.1667 - 1.1667i Is there some reason this returns the inverse of the diagonal entries, or am I completely missing something? Is returning the inverse something standard?? Since I'm new, I'm not quite sure where to look for actual source code. Is there a location where the LU factorization code is written and well commented? Thank you very much!
