/*! \file
Copyright (c) 2003, The Regents of the University of California, through
Lawrence Berkeley National Laboratory (subject to receipt of any required 
approvals from U.S. Dept. of Energy) 

All rights reserved. 

The source code is distributed under BSD license, see the file License.txt
at the top-level directory.
*/

/*
 * -- SuperLU routine (version 2.0) --
 * Univ. of California Berkeley, Xerox Palo Alto Research Center,
 * and Lawrence Berkeley National Lab.
 * November 15, 1997
 *
 */
#include <math.h>
#include "slu_sdefs.h"

int sgst01(int m, int n, SuperMatrix *A, SuperMatrix *L, 
		SuperMatrix *U, int *perm_c, int *perm_r, float *resid)
{
/* 
    Purpose   
    =======   

    SGST01 reconstructs a matrix A from its L*U factorization and   
    computes the residual   
       norm(L*U - A) / ( N * norm(A) * EPS ),   
    where EPS is the machine epsilon.   

    Arguments   
    ==========   

    M       (input) INT   
            The number of rows of the matrix A.  M >= 0.   

    N       (input) INT   
            The number of columns of the matrix A.  N >= 0.   

    A       (input) SuperMatrix *, dimension (A->nrow, A->ncol)
            The original M x N matrix A.   

    L       (input) SuperMatrix *, dimension (L->nrow, L->ncol)
            The factor matrix L.

    U       (input) SuperMatrix *, dimension (U->nrow, U->ncol)
            The factor matrix U.

    perm_c (input) INT array, dimension (N)
            The column permutation from SGSTRF.   

    perm_r  (input) INT array, dimension (M)
            The pivot indices from SGSTRF.   

    RESID   (output) FLOAT*
            norm(L*U - A) / ( N * norm(A) * EPS )   

    ===================================================================== 
*/  

    /* Local variables */
    float zero = 0.0;
    int i, j, k, arow, lptr,isub,  urow, superno, fsupc, u_part;
    float utemp, comp_temp;
    float anorm, tnorm, cnorm;
    float eps;
    float *work;
    SCformat *Lstore;
    NCformat *Astore, *Ustore;
    float *Aval, *Lval, *Uval;
    int *colbeg, *colend;

    /* Function prototypes */
    extern float slangs(char *, SuperMatrix *);

    /* Quick exit if M = 0 or N = 0. */

    if (m <= 0 || n <= 0) {
	*resid = 0.f;
	return 0;
    }

    work = (float *)floatCalloc(m);

    Astore = A->Store;
    Aval = Astore->nzval;
    Lstore = L->Store;
    Lval = Lstore->nzval;
    Ustore = U->Store;
    Uval = Ustore->nzval;

    colbeg = intMalloc(n);
    colend = intMalloc(n);

        for (i = 0; i < n; i++) {
            colbeg[perm_c[i]] = Astore->colptr[i]; 
	    colend[perm_c[i]] = Astore->colptr[i+1];
        }
	
    /* Determine EPS and the norm of A. */
    eps = smach("Epsilon");
    anorm = slangs("1", A);
    cnorm = 0.;

    /* Compute the product L*U, one column at a time */
    for (k = 0; k < n; ++k) {

	/* The U part outside the rectangular supernode */
        for (i = U_NZ_START(k); i < U_NZ_START(k+1); ++i) {
	    urow = U_SUB(i);
	    utemp = Uval[i];
            superno = Lstore->col_to_sup[urow];
	    fsupc = L_FST_SUPC(superno);
	    u_part = urow - fsupc + 1;
	    lptr = L_SUB_START(fsupc) + u_part;
            work[L_SUB(lptr-1)] -= utemp;   /* L_ii = 1 */
	    for (j = L_NZ_START(urow) + u_part; j < L_NZ_START(urow+1); ++j) {
                isub = L_SUB(lptr);
	        work[isub] -= Lval[j] * utemp;
	        ++lptr;
	    }
	}

	/* The U part inside the rectangular supernode */
	superno = Lstore->col_to_sup[k];
	fsupc = L_FST_SUPC(superno);
	urow = L_NZ_START(k);
	for (i = fsupc; i <= k; ++i) {
	    utemp = Lval[urow++];
	    u_part = i - fsupc + 1;
	    lptr = L_SUB_START(fsupc) + u_part;
            work[L_SUB(lptr-1)] -= utemp;   /* L_ii = 1 */
	    for (j = L_NZ_START(i)+u_part; j < L_NZ_START(i+1); ++j) {
                isub = L_SUB(lptr);
	        work[isub] -= Lval[j] * utemp;
	        ++lptr;
	    }
	}

	/* Now compute A[k] - (L*U)[k] (Both matrices may be permuted.) */

	for (i = colbeg[k]; i < colend[k]; ++i) {
	    arow = Astore->rowind[i];
	    work[perm_r[arow]] += Aval[i];
        }

	/* Now compute the 1-norm of the column vector work */
        tnorm = 0.;
	for (i = 0; i < m; ++i) {
	    tnorm += fabs(work[i]);
	    work[i] = zero;
	}
	cnorm = SUPERLU_MAX(tnorm, cnorm);
    }

    *resid = cnorm;

    if (anorm <= 0.f) {
	if (*resid != 0.f) {
	    *resid = 1.f / eps;
	}
    } else {
	*resid = *resid / (float) n / anorm / eps;
    }

    SUPERLU_FREE(work);
    SUPERLU_FREE(colbeg);
    SUPERLU_FREE(colend);
    return 0;

/*     End of SGST01 */

} /* sgst01_ */