[petsc-users] class templates in C++ and Petsc functions

[Umut Tabak]

Dear all,

I was trying to write a simple class template code to interface Petsc 
matrices along with Boost sparse matrices and vice versa. However, my 
first naive try did not work out of the box, since the template class 
requires some functions from PETSc libraries and these functions should 
be located in the object files to be able to compile. Since class 
template is header only and there is no object code generation, it can 
not find the PETSc library functions which is logical. I am also new to 
templates in C++. I just gave a try to create a template class instead 
of code duplication however it did not end up as expected. Are there 
some smarter ways to accomplish this task. The function analyzes a boost 
csr matrix and sets the rows of a Petsc matrix. T is for boost matrices
and T1 for Mat in Petsc. I can also get some comments on the code ;)

Best regards,
Umut

template <class T, class T1>
int converter<T, T1>::convertMBo2Pe( const T& A,
                                                                T1 A_ ){
     PetscErrorCode ierr;
     int cntNnz = 0;
     typedef typename T::iterator1 i1_t;
     typedef typename T::iterator2 i2_t;
     //int nnz[ooFelieMatrix.size1()];
     int nnz[A.size1()];
     unsigned ind=0;
     //get information about the matrix

     double* vals = NULL;
     for (i1_t i1 = A.begin1(); i1 != A.end1(); ++i1)
     {
       nnz[ind] = distance(i1.begin(), i1.end());
       ind++;
     }
     // create the matrix depending
     // on the values of the nonzeros
     // on each row
     ierr = MatCreateSeqAIJ( PETSC_COMM_SELF, A.size1(),
                                                   A.size2(), cntNnz, nnz,
                                                   A_ );
     PetscInt rInd = 0, cInd=0;
     PetscInt* rCount, dummy;
     rCount = &dummy;
     // pointer to values in a row
     PetscScalar*   valsOfRowI = NULL;
     PetscInt*  colIndexOfRowI = NULL;
     PetscInt rC = 1;
     for(i1_t i1 = A.begin1(); i1 != A.end1(); ++i1)
     {
       // allocate space for the values of row I
       valsOfRowI     = new PetscScalar[nnz[rInd]];
       colIndexOfRowI = new PetscInt[nnz[rInd]];
       for(i2_t i2 = i1.begin(); i2 != i1.end(); ++i2)
       {
          colIndexOfRowI[cInd] = i2.index2();
          valsOfRowI[cInd]     = *i2;
          cInd++;
       }
       // setting one row each time
       *rCount = rInd;
       MatSetValues( A_, rC, rCount, nnz[rInd],
                                   colIndexOfRowI, valsOfRowI,
                   INSERT_VALUES );
       // delete
       delete [] valsOfRowI;
       delete [] colIndexOfRowI;
       rInd++; cInd = 0;
     }
     //
     MatAssemblyBegin( A_, MAT_FINAL_ASSEMBLY );
     MatAssemblyEnd( A_, MAT_FINAL_ASSEMBLY );
     // return
     return 0;
}

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