/*! @file dlangs.c

 * \brief Returns the value of the one norm

 *

 * 

 * -- SuperLU routine (version 2.0) --

 * Univ. of California Berkeley, Xerox Palo Alto Research Center,

 * and Lawrence Berkeley National Lab.

 * November 15, 1997

 *

 * Modified from lapack routine DLANGE 

 * 

 */

/*

 * File name:	dlangs.c

 * History:     Modified from lapack routine DLANGE

 */

#include <math.h></math.h>

#include "slu_ddefs.h"

/*! \brief

 *

 * 

 * Purpose   

 *   =======   

 *

 *   DLANGS returns the value of the one norm, or the Frobenius norm, or 

 *   the infinity norm, or the element of largest absolute value of a 

 *   real matrix A.   

 *

 *   Description   

 *   ===========   

 *

 *   DLANGE returns the value   

 *

 *      DLANGE = ( max(abs(A(i,j))), NORM = 'M' or 'm'   

 *               (   

 *               ( norm1(A),         NORM = '1', 'O' or 'o'   

 *               (   

 *               ( normI(A),         NORM = 'I' or 'i'   

 *               (   

 *               ( normF(A),         NORM = 'F', 'f', 'E' or 'e'   

 *

 *   where  norm1  denotes the  one norm of a matrix (maximum column sum), 

 *   normI  denotes the  infinity norm  of a matrix  (maximum row sum) and 

 *   normF  denotes the  Frobenius norm of a matrix (square root of sum of 

 *   squares).  Note that  max(abs(A(i,j)))  is not a  matrix norm.   

 *

 *   Arguments   

 *   =========   

 *

 *   NORM    (input) CHARACTER*1   

 *           Specifies the value to be returned in DLANGE as described above.   

 *   A       (input) SuperMatrix*

 *           The M by N sparse matrix A. 

 *

 *  =====================================================================

 * 

 */

double dlangs(char *norm, SuperMatrix *A)

{

    /* Local variables */

    NCformat *Astore;

    double   *Aval;

    int      i, j, irow;

    double   value, sum;

    double   *rwork;

    Astore = A->Store;

    Aval   = Astore->nzval;

    if ( SUPERLU_MIN(A->nrow, A->ncol) == 0) {

	value = 0.;

    } else if (lsame_(norm, "M")) {

	/* Find max(abs(A(i,j))). */

	value = 0.;

	for (j = 0; j < A->ncol; ++j)

	    for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++)

		value = SUPERLU_MAX( value, fabs( Aval[i]) );

    } else if (lsame_(norm, "O") || *(unsigned char *)norm == '1') {

	/* Find norm1(A). */

	value = 0.;

	for (j = 0; j < A->ncol; ++j) {

	    sum = 0.;

	    for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++) 

		sum += fabs(Aval[i]);

	    value = SUPERLU_MAX(value,sum);

	}

    } else if (lsame_(norm, "I")) {

	/* Find normI(A). */

	if ( !(rwork = (double *) SUPERLU_MALLOC(A->nrow * sizeof(double))) )

	    ABORT("SUPERLU_MALLOC fails for rwork.");

	for (i = 0; i < A->nrow; ++i) rwork[i] = 0.;

	for (j = 0; j < A->ncol; ++j)

	    for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++) {

		irow = Astore->rowind[i];

		rwork[irow] += fabs(Aval[i]);

	    }

	value = 0.;

	for (i = 0; i < A->nrow; ++i)

	    value = SUPERLU_MAX(value, rwork[i]);

	SUPERLU_FREE (rwork);

    } else if (lsame_(norm, "F") || lsame_(norm, "E")) {

	/* Find normF(A). */

	ABORT("Not implemented.");

    } else

	ABORT("Illegal norm specified.");

    return (value);

} /* dlangs */