[petsc-users] From CSR format to MatSetValues

[w_ang_temp]

Hello,
    When solving a linear system Ax=b, the first step is assigning values to
matrix A. In my program, the subroutine PETSCSOLVE, which is used to slove Ax=b
with PETSc, gets the CSR format matrix(values, columns, rowIndex) to set values
to PETSc Mat A.
    The variables 'values'、'columns'、'rowIndex' belong to the main function.
They are used to represent a matrix in CSR format. The following table describes
the arrays in terms of the values, row, and column positions of the non-zero
elements in a sparse matrix.
    values: A real or complex array that contains the non-zero elements of a
            sparse matrix. The non-zero elements are mapped into the values
            array using the row-major upper triangular storage mapping described
            above.
    columns: Element i of the integer array columns is the number of the column
             that contains the i-th element in the values array.
    rowIndex: Element j of the integer array rowIndex gives the index of the
              element in the values array that is first non-zero element in a row j.

codes:
---------Set Values to A From CSR Format(values,rowIndex,columns)-------------------
      !values:Non-Symmetric Matrix
      ione = 1
      do 10,II=Istart+1,Iend
        !non-zero numbers of this row
        rowNum=rowIndex(II+1)-rowIndex(II)
        do 11,JJ=1,rowNum
       
            !elemnt index of the values/columns
            kValNn=rowIndex(II)+JJ-1
            !column index of this element
            nCol=columns(kValNn)-1
           
            !Setdata:II-RowIndex,nCol-ColIndex
            nRow=II-1
            call MatSetValues(A,ione,nRow,ione,nCol,values(kValNn),INSERT_VALUES,ierr)
  11    continue     
  10  continue
--------------------------------------------------------------------------------------

    As we can see, it has to loop a number of times because it can only set one data per
time. And this leads to low efficiency.
    So is there a better way to do this?
    Thank you.
                                      Jim
 
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