Multiply a dense vector with a sparse matrix.

dvsm_quad.c

#ifndef csi
#define csi ptrdiff_t
#endif
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>
 
typedef struct cs_sparse {
    csi nzmax;
    csi m;
    csi n;
    csi *p;
    csi *i;
    double *x;
    csi nz;
} cs;
 
double dvsm_quad(cs* Q, double* x) {
    int nzmax = Q->nz;
    unsigned int k;
    double ell = 0;
    for (k = 0; k < nzmax; k++) {
        int i = (Q->i)[k];
        int j = (Q->p)[k];        
        ell += (Q->x)[k] * x[i] * x[j];
    }
    printf("L_inside=%g\n",ell);
    return (ell);
}
 
/*
 * 
 */
int main(int argc, char** argv) {
        
    ptrdiff_t i[2]= {0,1};
    ptrdiff_t p[2]= {0,1};
    double vals[2]={1.0,1.0};
    cs* Q = malloc(sizeof(Q));
    double x[2] = {5.0, 5.0};
    
    Q->i=i;
    Q->p=p;
    Q->nz=2;
    Q->nzmax=2;
    Q->n=2;
    Q->m=2;
    Q->x=vals;
    
    double L= dvsm_quad(Q, x);
    printf("L_outside=%g\n",L);
    
    return (EXIT_SUCCESS);
 
}