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/*! @file dlangs.c
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 * \brief Returns the value of the one norm
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 *
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 * 
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 * -- SuperLU routine (version 2.0) --
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 * Univ. of California Berkeley, Xerox Palo Alto Research Center,
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 * and Lawrence Berkeley National Lab.
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 * November 15, 1997
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 *
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 * Modified from lapack routine DLANGE 
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 * 
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 */
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/*
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 * File name:	dlangs.c
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 * History:     Modified from lapack routine DLANGE
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 */
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#include <math.h></math.h>
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#include "slu_ddefs.h"
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/*! \brief
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 *
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 * 
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 * Purpose   
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 *   =======   
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 *
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 *   DLANGS returns the value of the one norm, or the Frobenius norm, or 
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 *   the infinity norm, or the element of largest absolute value of a 
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 *   real matrix A.   
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 *
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 *   Description   
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 *   ===========   
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 *
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 *   DLANGE returns the value   
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 *
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 *      DLANGE = ( max(abs(A(i,j))), NORM = 'M' or 'm'   
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 *               (   
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 *               ( norm1(A),         NORM = '1', 'O' or 'o'   
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 *               (   
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 *               ( normI(A),         NORM = 'I' or 'i'   
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 *               (   
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 *               ( normF(A),         NORM = 'F', 'f', 'E' or 'e'   
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 *
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 *   where  norm1  denotes the  one norm of a matrix (maximum column sum), 
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 *   normI  denotes the  infinity norm  of a matrix  (maximum row sum) and 
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 *   normF  denotes the  Frobenius norm of a matrix (square root of sum of 
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 *   squares).  Note that  max(abs(A(i,j)))  is not a  matrix norm.   
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 *
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 *   Arguments   
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 *   =========   
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 *
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 *   NORM    (input) CHARACTER*1   
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 *           Specifies the value to be returned in DLANGE as described above.   
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 *   A       (input) SuperMatrix*
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 *           The M by N sparse matrix A. 
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 *
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 *  =====================================================================
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 * 
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 */
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double dlangs(char *norm, SuperMatrix *A)
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{
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    /* Local variables */
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    NCformat *Astore;
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    double   *Aval;
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    int      i, j, irow;
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    double   value, sum;
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    double   *rwork;
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    Astore = A->Store;
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    Aval   = Astore->nzval;
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    if ( SUPERLU_MIN(A->nrow, A->ncol) == 0) {
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	value = 0.;
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    } else if (lsame_(norm, "M")) {
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	/* Find max(abs(A(i,j))). */
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	value = 0.;
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	for (j = 0; j < A->ncol; ++j)
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	    for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++)
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		value = SUPERLU_MAX( value, fabs( Aval[i]) );
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    } else if (lsame_(norm, "O") || *(unsigned char *)norm == '1') {
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	/* Find norm1(A). */
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	value = 0.;
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	for (j = 0; j < A->ncol; ++j) {
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	    sum = 0.;
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	    for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++) 
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		sum += fabs(Aval[i]);
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	    value = SUPERLU_MAX(value,sum);
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	}
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    } else if (lsame_(norm, "I")) {
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	/* Find normI(A). */
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	if ( !(rwork = (double *) SUPERLU_MALLOC(A->nrow * sizeof(double))) )
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	    ABORT("SUPERLU_MALLOC fails for rwork.");
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	for (i = 0; i < A->nrow; ++i) rwork[i] = 0.;
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	for (j = 0; j < A->ncol; ++j)
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	    for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++) {
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		irow = Astore->rowind[i];
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		rwork[irow] += fabs(Aval[i]);
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	    }
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	value = 0.;
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	for (i = 0; i < A->nrow; ++i)
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	    value = SUPERLU_MAX(value, rwork[i]);
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	SUPERLU_FREE (rwork);
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    } else if (lsame_(norm, "F") || lsame_(norm, "E")) {
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	/* Find normF(A). */
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	ABORT("Not implemented.");
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    } else
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	ABORT("Illegal norm specified.");
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    return (value);
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} /* dlangs */
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