cs_scatter.c

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#include "cs.h"
/* x = x + beta * A(:,j), where x is a dense vector and A(:,j) is sparse */
int cs_scatter (const cs *A, int j, double beta, int *w, double *x, int mark,
    cs *C, int nz)
{
    int i, p, *Ap, *Ai, *Ci ;
    double *Ax ;
    if (!CS_CSC (A) || !w || !CS_CSC (C)) return (-1) ;     /* check inputs */
    Ap = A->p ; Ai = A->i ; Ax = A->x ; Ci = C->i ;
    for (p = Ap [j] ; p < Ap [j+1] ; p++)
    {
        i = Ai [p] ;                            /* A(i,j) is nonzero */
        if (w [i] < mark)
        {
            w [i] = mark ;                      /* i is new entry in column j */
            Ci [nz++] = i ;                     /* add i to pattern of C(:,j) */
            if (x) x [i] = beta * Ax [p] ;      /* x(i) = beta*A(i,j) */
        }
        else if (x) x [i] += beta * Ax [p] ;    /* i exists in C(:,j) already */
    }
    return (nz) ;
}