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Re: still Schur complement

Dear Lisandro,

I'm not completelly sure what are you actually trying to do. It seems
you know how to actually compute the local Schur complement in a
entry-by-entry basis. In that case, your way is semms to be OK.

What do you mean with entry-by-entry basis? Anyway, I have the local Schur complement explicitely, in form of a matrix (or C++ vector).


However, you get a error because of a inner implementation detail of
MATIS.  Do de following: set the local-to-global mapping AFTER setting
the matrix type. This way, your code should now work.

Unfortunately, changing the order of the Mat-commands gives me the same error. I guess I found the origin of the problem:

I put it in the order below because I thought to avoid

[2]PETSC ERROR: Sum of local lengths 3916 does not equal global length 1958

which is due to the fact that in the case of 2 Subdomains and 2 processors, e.g., it is NPb=NPb_tot in the Schur system, instead of NPb=NPb_tot/2. However, I realize just now that the order of the Mat-commands has no influence on this, and that the error mentioned below has probably its origin there.

I have chosen MATIS because in the manual page of MatCreateIS() it is written "...m and n are NOT related to the size of the map", but maybe I understand this setence wrong? How can I choose m,n and M,N independently?



On 3/17/08, Kathrin Burckhardt <tribur@xxxxxxxxxxxxxxxxx> wrote: 
Dear all,

 My problem, once again and more concrete:

 I have given the local Schur matrices Si and I would like to set-up the
 global matrix S without assembling the Si on one processor.

 I thought "MATIS" is the suitable matrix type, but I don't succeed in
 using it. My code is:

     IS is;
     ISCreateGeneral(PETSC_COMM_SELF, NPb, &uBId_global[0], &is);
     ISLocalToGlobalMapping mapping;
     ISLocalToGlobalMappingCreateIS(is, &mapping);
     Mat Stot;
     MatCreate(PETSC_COMM_WORLD,&Stot);
     MatSetLocalToGlobalMapping(Stot, mapping);
     MatSetSizes(Stot,NPb,NPb,NPb_tot,NPb_tot);
     MatSetType(Stot,MATIS);
    //or, alternatively
    //MatCreateIS(PETSC_COMM_WORLD,NPb,NPb,NPb_tot,NPb_tot,mapping,&Stot);
     for(int i=0; i<NPb; i++)
       for(int j=0; j<NPb; j++)
        MatSetValuesLocal(Stot, 1, &i, 1, &j, &S(i+1,j+1), ADD_VALUES);

 And I got the error

 [1]PETSC ERROR: MatSetValuesLocal() line 1471 in
 src/mat/interface/matrix.c
 [1]PETSC ERROR: --------------------- Error Message
 ------------------------------------
 [1]PETSC ERROR: Object is in wrong state!
 [1]PETSC ERROR: Object Type not set: Argument # 1!

 Can you tell me what's wrong?