1 #include "cs.h"
2 /* ordering and symbolic analysis for a Cholesky factorization */
cs_schol(CS_INT order,const cs * A)3 css *cs_schol (CS_INT order, const cs *A)
4 {
5     CS_INT n, *c, *post, *P ;
6     cs *C ;
7     css *S ;
8     if (!CS_CSC (A)) return (NULL) ;        /* check inputs */
9     n = A->n ;
10     S = cs_calloc (1, sizeof (css)) ;       /* allocate result S */
11     if (!S) return (NULL) ;                 /* out of memory */
12     P = cs_amd (order, A) ;                 /* P = amd(A+A'), or natural */
13     S->pinv = cs_pinv (P, n) ;              /* find inverse permutation */
14     cs_free (P) ;
15     if (order && !S->pinv) return (cs_sfree (S)) ;
16     C = cs_symperm (A, S->pinv, 0) ;        /* C = spones(triu(A(P,P))) */
17     S->parent = cs_etree (C, 0) ;           /* find etree of C */
18     post = cs_post (S->parent, n) ;         /* postorder the etree */
19     c = cs_counts (C, S->parent, post, 0) ; /* find column counts of chol(C) */
20     cs_free (post) ;
21     cs_spfree (C) ;
22     S->cp = cs_malloc (n+1, sizeof (CS_INT)) ; /* allocate result S->cp */
23     S->unz = S->lnz = cs_cumsum (S->cp, c, n) ; /* find column pointers for L */
24     cs_free (c) ;
25     return ((S->lnz >= 0) ? S : cs_sfree (S)) ;
26 }
27