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