122 lines
3.9 KiB
C
122 lines
3.9 KiB
C
/*BHEADER**********************************************************************
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* Copyright (c) 2006 The Regents of the University of California.
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* Produced at the Lawrence Livermore National Laboratory.
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* Written by the HYPRE team. UCRL-CODE-222953.
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* All rights reserved.
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*
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* This file is part of HYPRE (see http://www.llnl.gov/CASC/hypre/).
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* Please see the COPYRIGHT_and_LICENSE file for the copyright notice,
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* disclaimer, contact information and the GNU Lesser General Public License.
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*
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* HYPRE is free software; you can redistribute it and/or modify it under the
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* terms of the GNU General Public License (as published by the Free Software
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* Foundation) version 2.1 dated February 1999.
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*
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* HYPRE is distributed in the hope that it will be useful, but WITHOUT ANY
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* WARRANTY; without even the IMPLIED WARRANTY OF MERCHANTABILITY or FITNESS
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* FOR A PARTICULAR PURPOSE. See the terms and conditions of the GNU General
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* Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* $Revision$
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***********************************************************************EHEADER*/
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#include "hypre_lapack.h"
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#include "f2c.h"
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/* Subroutine */ int dlassq_(integer *n, doublereal *x, integer *incx,
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doublereal *scale, doublereal *sumsq)
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{
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/* -- LAPACK auxiliary routine (version 3.0) --
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Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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Courant Institute, Argonne National Lab, and Rice University
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June 30, 1999
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Purpose
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=======
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DLASSQ returns the values scl and smsq such that
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( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
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where x( i ) = X( 1 + ( i - 1 )*INCX ). The value of sumsq is
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assumed to be non-negative and scl returns the value
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scl = max( scale, abs( x( i ) ) ).
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scale and sumsq must be supplied in SCALE and SUMSQ and
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scl and smsq are overwritten on SCALE and SUMSQ respectively.
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The routine makes only one pass through the vector x.
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Arguments
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=========
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N (input) INTEGER
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The number of elements to be used from the vector X.
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X (input) DOUBLE PRECISION array, dimension (N)
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The vector for which a scaled sum of squares is computed.
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x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
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INCX (input) INTEGER
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The increment between successive values of the vector X.
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INCX > 0.
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SCALE (input/output) DOUBLE PRECISION
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On entry, the value scale in the equation above.
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On exit, SCALE is overwritten with scl , the scaling factor
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for the sum of squares.
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SUMSQ (input/output) DOUBLE PRECISION
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On entry, the value sumsq in the equation above.
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On exit, SUMSQ is overwritten with smsq , the basic sum of
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squares from which scl has been factored out.
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=====================================================================
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Parameter adjustments */
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/* System generated locals */
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integer i__1, i__2;
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doublereal d__1;
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/* Local variables */
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static doublereal absxi;
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static integer ix;
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--x;
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/* Function Body */
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if (*n > 0) {
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i__1 = (*n - 1) * *incx + 1;
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i__2 = *incx;
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for (ix = 1; i__2 < 0 ? ix >= i__1 : ix <= i__1; ix += i__2) {
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if (x[ix] != 0.) {
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absxi = (d__1 = x[ix], abs(d__1));
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if (*scale < absxi) {
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/* Computing 2nd power */
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d__1 = *scale / absxi;
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*sumsq = *sumsq * (d__1 * d__1) + 1;
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*scale = absxi;
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} else {
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/* Computing 2nd power */
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d__1 = absxi / *scale;
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*sumsq += d__1 * d__1;
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}
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}
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/* L10: */
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}
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}
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return 0;
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/* End of DLASSQ */
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} /* dlassq_ */
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