54 lines
1.6 KiB
C
54 lines
1.6 KiB
C
#include "cs.h"
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/* x=A\b where A can be rectangular; b overwritten with solution */
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int cs_qrsol (int order, const cs *A, double *b)
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{
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double *x ;
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css *S ;
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csn *N ;
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cs *AT = NULL ;
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int k, m, n, ok ;
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if (!CS_CSC (A) || !b) return (0) ; /* check inputs */
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n = A->n ;
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m = A->m ;
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if (m >= n)
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{
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S = cs_sqr (order, A, 1) ; /* ordering and symbolic analysis */
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N = cs_qr (A, S) ; /* numeric QR factorization */
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x = cs_calloc (S ? S->m2 : 1, sizeof (double)) ; /* get workspace */
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ok = (S && N && x) ;
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if (ok)
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{
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cs_ipvec (S->pinv, b, x, m) ; /* x(0:m-1) = b(p(0:m-1) */
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for (k = 0 ; k < n ; k++) /* apply Householder refl. to x */
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{
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cs_happly (N->L, k, N->B [k], x) ;
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}
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cs_usolve (N->U, x) ; /* x = R\x */
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cs_ipvec (S->q, x, b, n) ; /* b(q(0:n-1)) = x(0:n-1) */
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}
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}
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else
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{
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AT = cs_transpose (A, 1) ; /* Ax=b is underdetermined */
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S = cs_sqr (order, AT, 1) ; /* ordering and symbolic analysis */
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N = cs_qr (AT, S) ; /* numeric QR factorization of A' */
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x = cs_calloc (S ? S->m2 : 1, sizeof (double)) ; /* get workspace */
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ok = (AT && S && N && x) ;
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if (ok)
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{
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cs_pvec (S->q, b, x, m) ; /* x(q(0:m-1)) = b(0:m-1) */
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cs_utsolve (N->U, x) ; /* x = R'\x */
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for (k = m-1 ; k >= 0 ; k--) /* apply Householder refl. to x */
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{
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cs_happly (N->L, k, N->B [k], x) ;
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}
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cs_pvec (S->pinv, x, b, n) ; /* b(0:n-1) = x(p(0:n-1)) */
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}
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}
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cs_free (x) ;
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cs_sfree (S) ;
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cs_nfree (N) ;
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cs_spfree (AT) ;
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return (ok) ;
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}
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