int cs_spsolve (cs *G, const cs *B, int k, int *xi, double *x, const int *pinv,
int lo)
{
int j, J, p, q, px, top, n, *Gp, *Gi, *Bp, *Bi ;
double *Gx, *Bx ;
if (!CS_CSC (G) || !CS_CSC (B) || !xi || !x) return (-1) ;
Gp = G->p ; Gi = G->i ; Gx = G->x ; n = G->n ;
Bp = B->p ; Bi = B->i ; Bx = B->x ;
top = cs_reach (G, B, k, xi, pinv) ; /* xi[top..n-1]=Reach(B(:,k)) */
for (p = top ; p < n ; p++) x [xi [p]] = 0 ; /* clear x */
for (p = Bp [k] ; p < Bp [k+1] ; p++) x [Bi [p]] = Bx [p] ; /* scatter B */
for (px = top ; px < n ; px++)
{
j = xi [px] ; /* x(j) is nonzero */
J = pinv ? (pinv [j]) : j ; /* j maps to col J of G */
if (J < 0) continue ; /* column J is empty */
x [j] /= Gx [lo ? (Gp [J]) : (Gp [J+1]-1)] ;/* x(j) /= G(j,j) */
p = lo ? (Gp [J]+1) : (Gp [J]) ; /* lo: L(j,j) 1st entry */
q = lo ? (Gp [J+1]) : (Gp [J+1]-1) ; /* up: U(j,j) last entry */
for ( ; p < q ; p++)
{
x [Gi [p]] -= Gx [p] * x [j] ; /* x(i) -= G(i,j) * x(j) */
}
}
return (top) ; /* return top of stack */
}
void mexFunction
(
int nargout,
mxArray *pargout [ ],
int nargin,
const mxArray *pargin [ ]
)
{
cs Lmatrix, Bmatrix, *L, *B ;
double *x ;
int k, i, j, top, *xi, *perm ;
if (nargout > 1 || nargin != 2)
{
mexErrMsgTxt ("Usage: x = cs_reach(L,b)") ;
}
/* get inputs */
L = cs_mex_get_sparse (&Lmatrix, 1, 1, pargin [0]) ;
B = cs_mex_get_sparse (&Bmatrix, 0, 1, pargin [1]) ;
cs_mex_check (0, L->n, 1, 0, 1, 1, pargin [1]) ;
perm = cs_malloc (L->n, sizeof (int)) ;
for (k = 0 ; k < L->n ; k++) perm [k] = k ;
xi = cs_calloc (3*L->n, sizeof (int)) ;
top = cs_reach (L, B, 0, xi, perm) ;
pargout [0] = mxCreateDoubleMatrix (L->n - top, 1, mxREAL) ;
x = mxGetPr (pargout [0]) ;
for (j = 0, i = top ; i < L->n ; i++, j++) x [j] = xi [i] ;
cs_free (xi) ;
cs_free (perm) ;
}
