/*! \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 psgst07(trans_t *trans, int_t n, int_t nrhs, SuperMatrix *A, float *b, 
	    int_t ldb, float *x, int_t ldx, float *xact, 
	    int_t ldxact, float *ferr, float *berr, float *reslts)
{
/*
 * -- SuperLU MT routine (version 2.0) --
 * Lawrence Berkeley National Lab, Univ. of California Berkeley,
 * and Xerox Palo Alto Research Center.
 * September 10, 2007
 *
 *  Purpose   
 *  =======   
 *
 *  psgst07() tests the error bounds from iterative refinement for the   
 *  computed solution to a system of equations op(A)*X = B, where A is a 
 *  general n by n matrix and op(A) = A or A**T, depending on TRANS.
 *  
 *  RESLTS(1) = test of the error bound   
 *            = norm(X - XACT) / ( norm(X) * FERR )   
 *  A large value is returned if this ratio is not less than one.   
 *
 *  RESLTS(2) = residual from the iterative refinement routine   
 *            = the maximum of BERR / ( (n+1)*EPS + (*) ), where   
 *              (*) = (n+1)*UNFL / (min_i (abs(op(A))*abs(X) +abs(b))_i ) 
 *
 *  Arguments   
 *  =========   
 *
 *  TRANS   (input) trans_t
 *          Specifies the form of the system of equations.   
 *          = NOTRANS: A * X = B     (No transpose)   
 *          = TRANS:   A**T * X = B  (Transpose)   
 *          = CONJ:    A**H * X = B  (Conjugate transpose = Transpose)   
 *
 *  N       (input) INT_T
 *          The number of rows of the matrices X and XACT.  N >= 0.   
 *
 *  NRHS    (input) INT_T   
 *          The number of columns of the matrices X and XACT.  NRHS >= 0. 
 *
 *  A       (input) SuperMatrix *, dimension (A->nrow, A->ncol)
 *          The original n by n matrix A.   
 *
 *  B       (input) DOUBLE PRECISION array, dimension (LDB,NRHS)   
 *          The right hand side vectors for the system of linear   
 *          equations.   
 *
 *  LDB     (input) INT_T   
 *          The leading dimension of the array B.  LDB >= max(1,N).   
 *
 *  X       (input) DOUBLE PRECISION array, dimension (LDX,NRHS)   
 *          The computed solution vectors.  Each vector is stored as a   
 *          column of the matrix X.   
 *
 *  LDX     (input) INT_T   
 *          The leading dimension of the array X.  LDX >= max(1,N).   
 *
 *  XACT    (input) DOUBLE PRECISION array, dimension (LDX,NRHS)   
 *          The exact solution vectors.  Each vector is stored as a   
 *          column of the matrix XACT.   
 *
 *  LDXACT  (input) INT_T   
 *          The leading dimension of the array XACT.  LDXACT >= max(1,N). 
 *
 *
 *  FERR    (input) DOUBLE PRECISION array, dimension (NRHS)   
 *          The estimated forward error bounds for each solution vector   
 *          X.  If XTRUE is the true solution, FERR bounds the magnitude 
 *          of the largest entry in (X - XTRUE) divided by the magnitude 
 *          of the largest entry in X.   
 *
 *  BERR    (input) DOUBLE PRECISION array, dimension (NRHS)   
 *          The componentwise relative backward error of each solution   
 *          vector (i.e., the smallest relative change in any entry of A 
 *
 *          or B that makes X an exact solution).   
 *
 *  RESLTS  (output) DOUBLE PRECISION array, dimension (2)   
 *          The maximum over the NRHS solution vectors of the ratios:   
 *          RESLTS(1) = norm(X - XACT) / ( norm(X) * FERR )   
 *          RESLTS(2) = BERR / ( (n+1)*EPS + (*) )   
 *
 *  ===================================================================== 
*/
    
    /* Table of constant values */
    int c__1 = 1;

    /* System generated locals */
    float d__1, d__2;

    /* Local variables */
    float diff, axbi;
    int_t    imax, irow;
    int_t    i, j, k;
    int      n__1;
    float unfl, ovfl;
    float xnorm;
    float errbnd;
    int_t    notran;
    float eps, tmp;
    float *rwork;
    float *Aval;
    NCformat *Astore;

    /* Function prototypes */
    extern int    lsame_(char *, char *);
    extern int    isamax_(int *, float *, int *);
    extern double slamch_(char *);

    /* Quick exit if N = 0 or NRHS = 0. */
    if ( n <= 0 || nrhs <= 0 ) {
	reslts[0] = 0.;
	reslts[1] = 0.;
	return 0;
    }

    eps = slamch_("Epsilon");
    unfl = slamch_("Safe minimum");
    ovfl   = 1. / unfl;
    notran = (trans == NOTRANS);

    rwork  = (float *) SUPERLU_MALLOC(n*sizeof(float));
    if ( !rwork ) SUPERLU_ABORT("SUPERLU_MALLOC fails for rwork");
    Astore = A->Store;
    Aval   = (float *) Astore->nzval;
    
    /* Test 1:  Compute the maximum of   
       norm(X - XACT) / ( norm(X) * FERR )   
       over all the vectors X and XACT using the infinity-norm. */

    errbnd = 0.;
    for (j = 0; j < nrhs; ++j) {
	n__1 = n;
	imax = isamax_(&n__1, &x[j*ldx], &c__1);
        d__1 = fabs(x[imax-1 + j*ldx]);
	xnorm = SUPERLU_MAX(d__1,unfl);
	diff = 0.;
	for (i = 0; i < n; ++i) {
            d__1 = fabs(x[i+j*ldx] - xact[i+j*ldxact]);
	    diff = SUPERLU_MAX(diff, d__1);
	}

	if (xnorm > 1.) {
	    goto L20;
	} else if (diff <= ovfl * xnorm) {
	    goto L20;
	} else {
	    errbnd = 1. / eps;
	    goto L30;
	}

L20:
#if 0	
	if (diff / xnorm <= ferr[j]) {
	    d__1 = diff / xnorm / ferr[j];
	    errbnd = SUPERLU_MAX(errbnd,d__1);
	} else {
	    errbnd = 1. / eps;
	}
#endif
	d__1 = diff / xnorm / ferr[j];
	errbnd = SUPERLU_MAX(errbnd,d__1);
	/*printf("Ferr: %f\n", errbnd);*/
L30:
	;
    }
    reslts[0] = errbnd;

    /* Test 2: Compute the maximum of BERR / ( (n+1)*EPS + (*) ), where 
       (*) = (n+1)*UNFL / (min_i (abs(op(A))*abs(X) + abs(b))_i ) */

    for (k = 0; k < nrhs; ++k) {
	for (i = 0; i < n; ++i) 
            rwork[i] = fabs( b[i + k*ldb] );
	if ( notran ) {
	    for (j = 0; j < n; ++j) {
                tmp = fabs( x[j + k*ldx] );
		for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; ++i) {
                    rwork[Astore->rowind[i]] += fabs(Aval[i]) * tmp;
                }
	    }
	} else {
	    for (j = 0; j < n; ++j) {
		tmp = 0.;
		for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; ++i) {
		    irow = Astore->rowind[i];
                    d__1 = fabs( x[irow + k*ldx] );
                    tmp += fabs(Aval[i]) * d__1;
		}
		rwork[j] += tmp;
	    }
	}

	axbi = rwork[0];
	for (i = 1; i < n; ++i) axbi = SUPERLU_MIN(axbi, rwork[i]);
	
	/* Computing MAX */
	d__1 = axbi, d__2 = (n + 1) * unfl;
	tmp = berr[k] / ((n + 1) * eps + (n + 1) * unfl / SUPERLU_MAX(d__1,d__2));
	
	if (k == 0) {
	    reslts[1] = tmp;
	} else {
	    reslts[1] = SUPERLU_MAX(reslts[1], tmp);
	}
    }

    SUPERLU_FREE(rwork);
    return 0;

} /* psgst07 */