# sparse matrix multiplication problem

## sparse matrix multiplication problem

Hi,
Please help me to resolve the problem with the calculation of product of two sparse matrices stored in the CSR format.
The following program computes the product C = A * B and returns an incorrect result.

double a[] = {1,2,2,3,1,1,4};
double b[] = {1,2,3,4,5,1,4};
int ja[] = {1,2,1,2,3,2,3};
int ia[] = {1,3,6,8};
int jb[] = {1,2,1,2,3,2,3};
int ib[] = {1,3,6,8};
double* c = NULL;
int* jc = NULL, * ic = NULL;

int m = 3;
double beta = 1.0;
char trans = 'N';
int request, sort;
int info;

ic = new int[m+1];
request = 1; sort = 0;
mkl_dcsrmultcsr(&trans, &request, &sort, &m, &m, &m, a, ja, ia, a, ja, ia, c, jc, ic, NULL, &info);
c = new double[ic[m]-1]; jc = new int[ic[m]-1];
request = 2;
mkl_dcsrmultcsr(&trans, &request, &sort, &m, &m, &m, a, ja, ia, a, ja, ia, c, jc, ic, NULL, &info);

Results:
c =  5       8       2       8      14       7       2       7      17
ic = 1       4       7      10
jc =  1       2       3       1       2       3       1       2       3

A = { 1 2 0
2 3 1
0 1 4 }

B = { 1 3 0
2 4 1
0 5 4 }

C = { 5 8  2
8 14 7
2 7  17 }  (incorrect 2nd column)

Best Regards,
Stan

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Thanks for letting us know your problem. I'm now trying to reproduce the issue, and I will update you as soon as I have some results.

Best,
Zhang

Hi, I figured out the problem. Your "b" array is incorrectly specified. It's not in the correct order for the CSR format. It should be {1,3,2,4,1,5,4}.

Zhang