Abdelrahman Said
220 lines
6.5 KiB
C
220 lines
6.5 KiB
C
/* -- translated by f2c (version 20240504).
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You must link the resulting object file with libf2c:
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on Microsoft Windows system, link with libf2c.lib;
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on Linux or Unix systems, link with .../path/to/libf2c.a -lm
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or, if you install libf2c.a in a standard place, with -lf2c -lm
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-- in that order, at the end of the command line, as in
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cc *.o -lf2c -lm
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Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
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http://www.netlib.org/f2c/libf2c.zip
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*/
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#include "f2c.h"
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/* > \brief \b DLARRA computes the splitting points with the specified threshold.
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=========== DOCUMENTATION ===========
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Online html documentation available at
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http://www.netlib.org/lapack/explore-html/
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> \htmlonly
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> Download DLARRA + dependencies
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> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlarra.
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f">
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> [TGZ]</a>
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> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlarra.
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f">
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> [ZIP]</a>
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> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlarra.
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f">
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> [TXT]</a>
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> \endhtmlonly
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Definition:
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===========
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SUBROUTINE DLARRA( N, D, E, E2, SPLTOL, TNRM,
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NSPLIT, ISPLIT, INFO )
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INTEGER INFO, N, NSPLIT
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DOUBLE PRECISION SPLTOL, TNRM
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INTEGER ISPLIT( * )
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DOUBLE PRECISION D( * ), E( * ), E2( * )
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> \par Purpose:
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=============
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>
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> \verbatim
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>
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> Compute the splitting points with threshold SPLTOL.
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> DLARRA sets any "small" off-diagonal elements to zero.
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> \endverbatim
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Arguments:
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==========
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> \param[in] N
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> \verbatim
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> N is INTEGER
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> The order of the matrix. N > 0.
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> \endverbatim
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>
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> \param[in] D
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> \verbatim
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> D is DOUBLE PRECISION array, dimension (N)
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> On entry, the N diagonal elements of the tridiagonal
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> matrix T.
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> \endverbatim
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>
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> \param[in,out] E
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> \verbatim
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> E is DOUBLE PRECISION array, dimension (N)
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> On entry, the first (N-1) entries contain the subdiagonal
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> elements of the tridiagonal matrix T; E(N) need not be set.
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> On exit, the entries E( ISPLIT( I ) ), 1 <= I <= NSPLIT,
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> are set to zero, the other entries of E are untouched.
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> \endverbatim
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>
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> \param[in,out] E2
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> \verbatim
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> E2 is DOUBLE PRECISION array, dimension (N)
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> On entry, the first (N-1) entries contain the SQUARES of the
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> subdiagonal elements of the tridiagonal matrix T;
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> E2(N) need not be set.
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> On exit, the entries E2( ISPLIT( I ) ),
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> 1 <= I <= NSPLIT, have been set to zero
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> \endverbatim
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>
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> \param[in] SPLTOL
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> \verbatim
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> SPLTOL is DOUBLE PRECISION
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> The threshold for splitting. Two criteria can be used:
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> SPLTOL<0 : criterion based on absolute off-diagonal value
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> SPLTOL>0 : criterion that preserves relative accuracy
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> \endverbatim
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>
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> \param[in] TNRM
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> \verbatim
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> TNRM is DOUBLE PRECISION
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> The norm of the matrix.
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> \endverbatim
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>
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> \param[out] NSPLIT
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> \verbatim
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> NSPLIT is INTEGER
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> The number of blocks T splits into. 1 <= NSPLIT <= N.
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> \endverbatim
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>
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> \param[out] ISPLIT
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> \verbatim
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> ISPLIT is INTEGER array, dimension (N)
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> The splitting points, at which T breaks up into blocks.
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> The first block consists of rows/columns 1 to ISPLIT(1),
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> the second of rows/columns ISPLIT(1)+1 through ISPLIT(2),
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> etc., and the NSPLIT-th consists of rows/columns
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> ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N.
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> \endverbatim
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>
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> \param[out] INFO
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> \verbatim
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> INFO is INTEGER
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> = 0: successful exit
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> \endverbatim
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Authors:
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========
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> \author Univ. of Tennessee
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> \author Univ. of California Berkeley
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> \author Univ. of Colorado Denver
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> \author NAG Ltd.
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> \date September 2012
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> \ingroup auxOTHERauxiliary
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> \par Contributors:
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==================
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>
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> Beresford Parlett, University of California, Berkeley, USA \n
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> Jim Demmel, University of California, Berkeley, USA \n
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> Inderjit Dhillon, University of Texas, Austin, USA \n
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> Osni Marques, LBNL/NERSC, USA \n
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> Christof Voemel, University of California, Berkeley, USA
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=====================================================================
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Subroutine */ int igraphdlarra_(integer *n, doublereal *d__, doublereal *e,
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doublereal *e2, doublereal *spltol, doublereal *tnrm, integer *nsplit,
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integer *isplit, integer *info)
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{
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/* System generated locals */
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integer i__1;
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doublereal d__1, d__2;
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/* Builtin functions */
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double sqrt(doublereal);
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/* Local variables */
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integer i__;
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doublereal tmp1, eabs;
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/* -- LAPACK auxiliary routine (version 3.4.2) --
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-- LAPACK is a software package provided by Univ. of Tennessee, --
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-- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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September 2012
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=====================================================================
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Parameter adjustments */
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--isplit;
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--e2;
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--e;
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--d__;
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/* Function Body */
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*info = 0;
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/* Compute splitting points */
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*nsplit = 1;
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if (*spltol < 0.) {
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/* Criterion based on absolute off-diagonal value */
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tmp1 = abs(*spltol) * *tnrm;
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i__1 = *n - 1;
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for (i__ = 1; i__ <= i__1; ++i__) {
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eabs = (d__1 = e[i__], abs(d__1));
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if (eabs <= tmp1) {
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e[i__] = 0.;
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e2[i__] = 0.;
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isplit[*nsplit] = i__;
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++(*nsplit);
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}
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/* L9: */
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}
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} else {
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/* Criterion that guarantees relative accuracy */
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i__1 = *n - 1;
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for (i__ = 1; i__ <= i__1; ++i__) {
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eabs = (d__1 = e[i__], abs(d__1));
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if (eabs <= *spltol * sqrt((d__1 = d__[i__], abs(d__1))) * sqrt((
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d__2 = d__[i__ + 1], abs(d__2)))) {
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e[i__] = 0.;
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e2[i__] = 0.;
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isplit[*nsplit] = i__;
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++(*nsplit);
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}
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/* L10: */
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}
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}
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isplit[*nsplit] = *n;
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return 0;
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/* End of DLARRA */
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} /* igraphdlarra_ */
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