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#include "cs.h"
/* apply the ith Householder vector to x */
csi cs_happly (const cs *V, csi i, double beta, double *x)
{
csi p, *Vp, *Vi ;
double *Vx, tau = 0 ;
if (!CS_CSC (V) || !x) return (0) ; /* check inputs */
Vp = V->p ; Vi = V->i ; Vx = V->x ;
for (p = Vp [i] ; p < Vp [i+1] ; p++) /* tau = v'*x */
{
tau += Vx [p] * x [Vi [p]] ;
}
tau *= beta ; /* tau = beta*(v'*x) */
for (p = Vp [i] ; p < Vp [i+1] ; p++) /* x = x - v*tau */
{
x [Vi [p]] -= Vx [p] * tau ;
}
return (1) ;
}
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