[petsc-users] MATMPIBAIJ matrix allocation

[Heikki Virtanen]

> El 29/07/2013, a las 14:54, Heikki Virtanen escribió:
> 
> > Hi, I try to solve an eigenvalue problem (Ax = lambda B x) where A 
> > and B are complex matrices. Unfortunately, my data structures 
> > are not capable of handling directly complex numbers, yet. So,
> > I have to use 
> > 
> >                 [re(A) -im(A)]
> > RealA  = [                    ]
> >                 [imA)   re(A)] 
> > 
> > matrices instead. How should I allocate matrices if I know
> > compressed sparse row matrix formats of A and B matrices. I have used
> > something like this.
> > 
> > ierr = MatCreate(PETSC_COMM_WORLD,&RealA); CHKERRQ(ierr);    
> > ierr = MatSetSizes(RealA,PETSC_DECIDE,PETSC_DECIDE,2*n,2*n); CHKERRQ(ierr);
> > ierr = MatSetType(RealA,MATMPIBAIJ); CHKERRQ(ierr);
> > ierr = MatSetBlockSize(RealA,2);CHKERRQ(ierr);
> > ierr = MatSetFromOptions(RealA);CHKERRQ(ierr);
> >                 
> > ierr = MatMPIBAIJSetPreallocationCSR (RealA,2,rows,cols,0); CHKERRQ(ierr);
> > ierr = MatAssemblyBegin (RealA,MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
> > ierr = MatAssemblyEnd (RealA,MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
> > 
> > where n is the global size of matrix A. rows and cols are csr arrays of A.
> > Each submatrix of RealA matrix have the same nonzero pattern than A.
> > But I am not sure if this is correct, because when I print my matrices out
> > they look more like band matrices than block matrices.
> > 
> > -Heikki
> 
> You are creating a BAIJ matrix with the nonzero pattern defined by (rows,cols), where each entry of the matrix is a 2x2 block, in your case
>            [ re(a_ij) -im(a_ij) ]
>            [ im(a_ij)  re(a_ij) ]
> 
> So the matrix you are creating is not this one
>                 [re(A) -im(A)]
>                 [imA)   re(A)]
> but the one resulting from a perfect shuffle permutation. That's why you are not seeing a 2x2 block structure for the whole matrix.
> 
> Jose
> 

Hi, Sorry to bother you, but I still have problems with MATMPIBAIJ matrices. It is said here

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateBAIJ.html

that these matrices are created using block compressed row format. It means this one

http://www.cs.colostate.edu/~mroberts/toolbox/c++/sparseMatrix/sparse_matrix_compression.html

or something else? (indices start here from 1 not from 0, but if this is fixed, then the format should be the same?)
I have also second question. What does "block size" mean? Is it number of elements per side of the Block?

-Heikki 
 		 	   		  
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