/*! \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.
*/

#include <math.h>
#include "slu_mt_sdefs.h"

int_t psgst01(int_t m, int_t n, SuperMatrix *A, SuperMatrix *L, 
	    SuperMatrix *U, int_t *perm_c, int_t *perm_r, float *resid)
{
/*
 * -- SuperLU MT routine (version 2.0) --
 * Lawrence Berkeley National Lab, Univ. of California Berkeley,
 * and Xerox Palo Alto Research Center.
 * September 10, 2007
 *
 *  Purpose   
 *  =======   
 *  psgst01() 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_T   
 *          The number of rows of the matrix A.  M >= 0.  
 *
 *   N      (input) INT_T   
 *          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_T array, dimension (N)
 *          The column permutation from SGSTRF.   
 *
 *   perm_r (input) INT_T array, dimension (M)
 *          The pivot indices from SGSTRF.
 *
 *   RESID  (output) DOUBLE*
 *          norm(L*U - A) / ( N * norm(A) * EPS )   
 *
 *   ===================================================================== 
 */
    /* Local variables */
    float      zero = 0.0;
    int_t i, j, k, arow, lptr,isub,  urow, superno, fsupc, u_part;
    float utemp, comp_temp;
    float anorm, tnorm, cnorm;
    float eps;
    float *work;
    NCformat *Astore;
    SCPformat *Lstore;
    NCPformat *Ustore;
    float *Aval, *Lval, *Uval;
    int_t *colbeg, *colend;

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


    /* 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;

    /* Determine EPS and the norm of A. */
    eps = slamch_("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_END(k); ++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_END(urow); ++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_END(i); ++j) {
                isub = L_SUB(lptr);
                work[isub] -= Lval[j] * utemp;
	        ++lptr;
	    }
	}

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

	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];
	}
	
	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 SP_SGET01 */

} /* psgst01 */