Question

Good day everyone,

I’m new in C programming and I don’t have a lot of knowledge on how to handle very huge matrix in C. e.g. Matrix size of 30.000 x 30.000.

My first approach is to store dynamically memory:

int main()
{      int **mat;
    int j;
    mat = (int **)malloc(R*sizeof(int*));
    for(j=0;j<R;j++)
        mat[j]=(int*)malloc(P*sizeof(int));
}

And it is a good idea to handle +/- matrix of 8.000 x 8.000. But, not bigger. So, I want to ask for any light to handle this kind of huge matrix, please.

As I said before: I am new to C, so please don’t expect too much experience.

Thanks in advance for any suggestion,

David Alejandro.

PD: My laptop conf is linux ubuntu, 64bit, i7, and 4gb of ram.

Answer 1

For a matrix as large as that, I would try to avoid all those calls to malloc. This will reduce the time to set up the datastructure and remove the memory overhead with dynamic memory (malloc stores additional information as to the size of the chunk)

Just use malloc once – i.e:

#include <stdlib.h>
int *matrix = malloc(R * P * sizeof(int));

Then to compute the index as

index = column + row * P;

Also access the memory sequentially i.e. by column first. Better performance for the cache.