[petsc-users] From CSR format to MatSetValues

[w_ang_temp]

Thanks very much. And I will have a try.
                                 Jim





At 2012-06-09 06:10:50,"Barry Smith" <bsmith at mcs.anl.gov> wrote:
>
>http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateSeqAIJWithArrays.html
>http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateMPIAIJWithArrays.html
>
>
>
>On Jun 8, 2012, at 1:31 AM, w_ang_temp wrote:
>
>> 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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