CBLAS segmenation fault with large array - c++

Question

this is my third post and attempt to solve this problem, which first
showed up using numpy.dot(A, A.T) where A is large, 150,000 x 265 elements.
With numpy, I got back an array with many missing values, that were just zeros.
I've tried to call BLAS thru CBLAS. I'm getting a segmentation fault error
with large arrays.
I'm running this on a machine with about 250 GB free memory.
Thanks for reading...
#include <stdio.h> /* I/O lib ISOC */
#include <stdlib.h> /* Standard Lib ISOC */
#include <cblas.h> /* C BLAS BLAS */
#include "blaio.h"
int main(int argc, char **argv) {
int row = 100000;
int col = 265;
float *a, *b, *c;
a = (float *) malloc(row * col * sizeof(float));
b = (float *) malloc(row * col * sizeof(float));
c = (float *) malloc(row * row * sizeof(float));
int i, end;
end = row * col;
for(i=0; i<end; i++)
{
a[i] = 1.0;
b[i] = 1.0;
}
for(i=0; i<(row*row); i++)
c[i] = 2.0;
// row_order transform transform rowsA colsB K alpha a lda b ldb beta c ldc
cblas_sgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans, row, row, col, 1.0f, a, col, b, row, 0.0f, c, row);
int num_bad = 0;
for(i=0; i<(row*row); i++)
{
if (c[i] != col)
{
printf("Bad value found: %f, at index: %i\n", c[i], i );
num_bad += 1;
}
}
printf("Number of bad values found: %i \n\n", num_bad);
//printMatrix(CblasRowMajor, row, row, c, 8, 3, NULL, NULL, NULL, NULL, NULL, "c = ");
return 0;
} /* end func main */
UPDATE:
Ray has expertly noticed that the blas I'm using via cblas, must be 32 bit and not able to access the array indices. Therefore, I've installed blas64.x86_64 and blas64-devel.x86_64.
Then, rewrote a few lines of the code above to use the direct call to sgemm without cblas.
#include <stdio.h> /* I/O lib ISOC */
#include <stdlib.h> /* Standard Lib ISOC */
int main(int argc, char **argv) {
int row = 100000;
int col = 265;
float *a, *b, *c;
a = (float *) malloc(row * col * sizeof(float));
b = (float *) malloc(row * col * sizeof(float));
c = (float *) malloc(row * row * sizeof(float));
int i, end;
end = row * col;
for(i=0; i<end; i++)
{
a[i] = 1.0;
b[i] = 1.0;
}
for(i=0; i<(row*row); i++)
c[i] = 2.0;
float alpha = 1.0, beta = 1.0;
sgemm_('N','N', &row, &row, &col, &alpha, &a[0], &col, &b[0], &row, &beta, &c[0], &row);
I compiled with:
gcc sgemm_test_fortran.c -o test -L /usr/lib64 -lblas64
The code compiled and I think it might run.. :)

Answer 1

The problem is that the size of your output matrix (100,000x100,000 = 1e10 elements) can't be stored in an int (2.14e9). You can fix this in your C++ code by switching the types to size_t, but you're going to run into the same problem inside the BLAS library.
What you need to to do is use a BLAS library that is compiled to use 8-byte integers; most BLAS libraries are compiled with 4-byte integers. You don't mention what BLAS library you're linking to, so it's hard to guess what the correct library name is (if it even exists) on your system.