cula use of culaSgels - wrong argument? - lapack

Question

I am trying to use the culaSgels function in order to solve Ax=B.
I modified the systemSolve example of the cula package.
void culaFloatExample()
{
int N=2;
int NRHS = 2;
int i,j;
double cula_time,start_time,end_time;
culaStatus status;
culaFloat* A = NULL;
culaFloat* B = NULL;
culaFloat* X = NULL;
culaFloat one = 1.0f;
culaFloat thresh = 1e-6f;
culaFloat diff;
printf("Allocating Matrices\n");
A = (culaFloat*)malloc(N*N*sizeof(culaFloat));
B = (culaFloat*)malloc(N*N*sizeof(culaFloat));
X = (culaFloat*)malloc(N*N*sizeof(culaFloat));
if(!A || !B )
exit(EXIT_FAILURE);
printf("Initializing CULA\n");
status = culaInitialize();
checkStatus(status);
// Set A
A[0]=1;
A[1]=2;
A[2]=3;
A[3]=4;
// Set B
B[0]=5;
B[1]=6;
B[2]=2;
B[3]=3;
printf("Calling culaSgels\n");
// Run CULA's version
start_time = getHighResolutionTime();
status = culaSgels('N',N,N, NRHS, A, N, A, N);
end_time = getHighResolutionTime();
cula_time = end_time - start_time;
checkStatus(status);
printf("Verifying Result\n");
for(i = 0; i < N; ++i){
for (j=0;j<N;j++)
{
diff = X[i+j*N] - B[i+j*N];
if(diff < 0.0f)
diff = -diff;
if(diff > thresh)
printf("\nResult check failed: X[%d]=%f B[%d]=%f\n", i, X[i+j*N],i, B[i+j*N]);
printf("\nResults:X= %f \t B= %f:\n",X[i+j*N],B[i+j*N]);
}
}
printRuntime(cula_time);
printf("Shutting down CULA\n\n");
culaShutdown();
free(A);
free(B);
}
I am using culaSgels('N',N,N, NRHS, A, N, A, N); to solve the system but :
1) The results show me that every element of X=0 , but B is right.
Also , it shows me the
Result check failed message
2) Studying the reference manual ,it says that one argument before the last argument (the A I have) ,should be the matrix B stored columnwised,but if I use "B" instead of "A" as parameter ,then I am not getting the correct B matrix.

Answer 1

Ok,code needs 3 things to work.
1) Change A to B ,so culaSgels('N',N,N, NRHS, A, N, B, N);
(I misunderstood that at exit B contains the solution)
2) Because CULA uses column major change A,B matrices accordingly.
3) Change to :
B = (culaFloat*)malloc(N*NRHS*sizeof(culaFloat));
X = (culaFloat*)malloc(N*NRHS*sizeof(culaFloat));
(use NHRS and not N which is the same in this example)
Thanks!