why I am getting this result in last half of array? - c

Question

Can anyone tell me why the output ( Anew ) is:
Anew = 0.000000
Anew = 2.000000
Anew = 4.000000
Anew = 6.000000
Anew = 16.000000
Anew = 20.000000
Anew = 24.000000
Anew = 28.000000
and not :
Anew = 0.000000
Anew = 2.000000
Anew = 4.000000
Anew = 6.000000
Anew = 8.000000
Anew = 10.000000
Anew = 12.000000
Anew = 14.000000
Code:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <mkl.h>
int main(int argc, const char* argv[]) {
int rows = 2, cols = 2, Layers = 2;
int PerLayerElmts = rows * cols;
float* A = malloc(PerLayerElmts * Layers * sizeof(*A));
// create A matrix
int ImagIdx;
for (int n = 0; n < Layers; n++) {
ImagIdx = 0;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
A[n * PerLayerElmts + ImagIdx] = n * PerLayerElmts + ImagIdx;
ImagIdx++;
}
}
}
// print A matrix
for (int n = 0; n < Layers; n++) {
ImagIdx = 0;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
printf("\nA = %f", A[n * PerLayerElmts + ImagIdx]);
ImagIdx++;
}
}
}
float scalar = 2.0;
size_t AddressOffset = 0;
for (int i = 0; i < Layers; i++, AddressOffset += PerLayerElmts) {
// multiply A by scalar
cblas_sscal(PerLayerElmts * Layers, scalar, A + AddressOffset, 1);
}
// print A matrix
for (int n = 0; n < Layers; n++) {
ImagIdx = 0;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
printf("\n\nAnew = %f", A[n * PerLayerElmts + ImagIdx]);
ImagIdx++;
}
}
}
printf("\n");
free(A);
return 0;
}
I am just creating a matrix and then using cblas call to multiply every element by a scalar ( 2 ).
I am doing that , using an addressoffset for the number of layers.
The problem is at the second layer where the elements are multiply by 4 and not 2!

Answer 1

Your way of calling cblas_sscal doesn't seem right. Instead of
cblas_sscal( PerLayerElmts * Layers , scalar , A + AddressOffset , 1 );
I would expect something like
cblas_sscal( PerLayerElmts , scalar , A + AddressOffset , 1 );
since you're calling it once for every layer.