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#include "cs_mex.h"
/* find nonzero pattern of x=L\sparse(b). L must be sparse, real, and lower
* triangular. b must be a real sparse vector. */
static
void dfsr (int j, const cs *L, int *top, int *xi, int *w)
{
int p ;
w [j] = 1 ; /* mark node j */
for (p = L->p [j] ; p < L->p [j+1] ; p++) /* for each i in L(:,j) */
{
if (w [L->i [p]] != 1) /* if i is unmarked */
{
dfsr (L->i [p], L, top, xi, w) ; /* start a dfs at i */
}
}
xi [--(*top)] = j ; /* push j onto the stack */
}
/* w [0..n-1] == 0 on input, <= 1 on output. size n */
static
int reachr (const cs *L, const cs *B, int *xi, int *w)
{
int p, n = L->n ;
int top = n ; /* stack is empty */
for (p = B->p [0] ; p < B->p [1] ; p++) /* for each i in pattern of b */
{
if (w [B->i [p]] != 1) /* if i is unmarked */
{
dfsr (B->i [p], L, &top, xi, w) ; /* start a dfs at i */
}
}
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 i, j, top, *xi ;
if (nargout > 1 || nargin != 2)
{
mexErrMsgTxt ("Usage: x = cs_reachr(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]) ;
xi = cs_calloc (2*L->n, sizeof (int)) ;
top = reachr (L, B, xi, xi + L->n) ;
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) ;
}
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