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Collins__Andrew
Beginner
87 Views

cblas_zsyrk returns wrong results

I have the following function and I'm trying to compute C = A*A' using zsyrk from blas, but when I print the C matrix the results are wrong. What am I missing?

double* zsyrk(int N, double *A) {

	int i,j;

	int K;
	K = N;

	const int * alpha;
	int a = 1;
	alpha = &a;

	int lda = N;
	int ldc = N;

	const int * beta;
	int b = 0;
	beta = &b;

	double *C;
	C = (double *)calloc( N*N, sizeof(double));

	for (i = 0; i < N; i++){
		for(j = 0; j < N; j++){
			printf("%lf ", A[i*N + j]);
		}
		printf("\n");
	}

	cblas_zsyrk(CblasRowMajor, CblasUpper, CblasTrans, N, K, alpha, A, lda, beta, C, ldc);

	for (i = 0; i < N; i++){
		for(j = 0; j < N; j++){
			printf("%lf ", C[i*N + j]);
		}
		printf("\n");
	}
	
	return C;
}

The restults are:

Matrix A:

-662.059957 -942.824833
545.621059 -270.699577

Matrix C:
-0.000000 0.000000
0.000000 -0.000000

 

0 Kudos
3 Replies
Ying_H_Intel
Employee
87 Views

Hi Andrews,

are the array A complex number or double array?
How about try cblas_dsyrk  to replace the cblas_zsyrk

Best regards,
Ying

 

BLAS routine names have the following structure:
<character> <name> <mod> ( )
The <character> field indicates the data type:

s real, single precision
c complex, single precision

 

d real, double precision
z complex, double precision


 

 

G__Petru
Beginner
87 Views

Hej, 

First of all please read the documentation more careful next time.

Instead of int declare both  constants, alpha and beta, as double

e.g.

const double * alpha;
09     double a = 1;
10     alpha = &a;

 

Also, in order to calculate C as C = A*A' (+yada yada) ,  you have to use CblasNoTrans instead of CblasTrans (check the documentation).

Now everything will work just as intended.

Regards,

Petru

G__Petru
Beginner
87 Views

Hej,

First of all, please read the documentation[0] more carefully next time.

In order to calculate correctly you have to:

1. change the alpha and beta constants from int to double.

e.g.

1     const double * alpha;
2     double a = 1;
3     alpha = &a;
 
 
4  
5     const double * beta;
6     double b = 0;
7

    beta = &b;

 

2. change CblasTrans to CblasNoTrans (check the documentation[0])

[0]:https://software.intel.com/en-us/mkl-developer-reference-c-cblas-syrk

Regards,

Petru

 
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