183 lines
4.8 KiB
Fortran
183 lines
4.8 KiB
Fortran
*> \brief \b DPTTRS
|
|
*
|
|
* =========== DOCUMENTATION ===========
|
|
*
|
|
* Online html documentation available at
|
|
* http://www.netlib.org/lapack/explore-html/
|
|
*
|
|
*> \htmlonly
|
|
*> Download DPTTRS + dependencies
|
|
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dpttrs.f">
|
|
*> [TGZ]</a>
|
|
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dpttrs.f">
|
|
*> [ZIP]</a>
|
|
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dpttrs.f">
|
|
*> [TXT]</a>
|
|
*> \endhtmlonly
|
|
*
|
|
* Definition:
|
|
* ===========
|
|
*
|
|
* SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
|
|
*
|
|
* .. Scalar Arguments ..
|
|
* INTEGER INFO, LDB, N, NRHS
|
|
* ..
|
|
* .. Array Arguments ..
|
|
* DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
|
|
* ..
|
|
*
|
|
*
|
|
*> \par Purpose:
|
|
* =============
|
|
*>
|
|
*> \verbatim
|
|
*>
|
|
*> DPTTRS solves a tridiagonal system of the form
|
|
*> A * X = B
|
|
*> using the L*D*L**T factorization of A computed by DPTTRF. D is a
|
|
*> diagonal matrix specified in the vector D, L is a unit bidiagonal
|
|
*> matrix whose subdiagonal is specified in the vector E, and X and B
|
|
*> are N by NRHS matrices.
|
|
*> \endverbatim
|
|
*
|
|
* Arguments:
|
|
* ==========
|
|
*
|
|
*> \param[in] N
|
|
*> \verbatim
|
|
*> N is INTEGER
|
|
*> The order of the tridiagonal matrix A. N >= 0.
|
|
*> \endverbatim
|
|
*>
|
|
*> \param[in] NRHS
|
|
*> \verbatim
|
|
*> NRHS is INTEGER
|
|
*> The number of right hand sides, i.e., the number of columns
|
|
*> of the matrix B. NRHS >= 0.
|
|
*> \endverbatim
|
|
*>
|
|
*> \param[in] D
|
|
*> \verbatim
|
|
*> D is DOUBLE PRECISION array, dimension (N)
|
|
*> The n diagonal elements of the diagonal matrix D from the
|
|
*> L*D*L**T factorization of A.
|
|
*> \endverbatim
|
|
*>
|
|
*> \param[in] E
|
|
*> \verbatim
|
|
*> E is DOUBLE PRECISION array, dimension (N-1)
|
|
*> The (n-1) subdiagonal elements of the unit bidiagonal factor
|
|
*> L from the L*D*L**T factorization of A. E can also be regarded
|
|
*> as the superdiagonal of the unit bidiagonal factor U from the
|
|
*> factorization A = U**T*D*U.
|
|
*> \endverbatim
|
|
*>
|
|
*> \param[in,out] B
|
|
*> \verbatim
|
|
*> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
|
|
*> On entry, the right hand side vectors B for the system of
|
|
*> linear equations.
|
|
*> On exit, the solution vectors, X.
|
|
*> \endverbatim
|
|
*>
|
|
*> \param[in] LDB
|
|
*> \verbatim
|
|
*> LDB is INTEGER
|
|
*> The leading dimension of the array B. LDB >= max(1,N).
|
|
*> \endverbatim
|
|
*>
|
|
*> \param[out] INFO
|
|
*> \verbatim
|
|
*> INFO is INTEGER
|
|
*> = 0: successful exit
|
|
*> < 0: if INFO = -k, the k-th argument had an illegal value
|
|
*> \endverbatim
|
|
*
|
|
* Authors:
|
|
* ========
|
|
*
|
|
*> \author Univ. of Tennessee
|
|
*> \author Univ. of California Berkeley
|
|
*> \author Univ. of Colorado Denver
|
|
*> \author NAG Ltd.
|
|
*
|
|
*> \date September 2012
|
|
*
|
|
*> \ingroup doublePTcomputational
|
|
*
|
|
* =====================================================================
|
|
SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
|
|
*
|
|
* -- LAPACK computational routine (version 3.4.2) --
|
|
* -- LAPACK is a software package provided by Univ. of Tennessee, --
|
|
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
|
|
* September 2012
|
|
*
|
|
* .. Scalar Arguments ..
|
|
INTEGER INFO, LDB, N, NRHS
|
|
* ..
|
|
* .. Array Arguments ..
|
|
DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
|
|
* ..
|
|
*
|
|
* =====================================================================
|
|
*
|
|
* .. Local Scalars ..
|
|
INTEGER J, JB, NB
|
|
* ..
|
|
* .. External Functions ..
|
|
INTEGER ILAENV
|
|
EXTERNAL ILAENV
|
|
* ..
|
|
* .. External Subroutines ..
|
|
EXTERNAL DPTTS2, XERBLA
|
|
* ..
|
|
* .. Intrinsic Functions ..
|
|
INTRINSIC MAX, MIN
|
|
* ..
|
|
* .. Executable Statements ..
|
|
*
|
|
* Test the input arguments.
|
|
*
|
|
INFO = 0
|
|
IF( N.LT.0 ) THEN
|
|
INFO = -1
|
|
ELSE IF( NRHS.LT.0 ) THEN
|
|
INFO = -2
|
|
ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
|
|
INFO = -6
|
|
END IF
|
|
IF( INFO.NE.0 ) THEN
|
|
CALL XERBLA( 'DPTTRS', -INFO )
|
|
RETURN
|
|
END IF
|
|
*
|
|
* Quick return if possible
|
|
*
|
|
IF( N.EQ.0 .OR. NRHS.EQ.0 )
|
|
$ RETURN
|
|
*
|
|
* Determine the number of right-hand sides to solve at a time.
|
|
*
|
|
IF( NRHS.EQ.1 ) THEN
|
|
NB = 1
|
|
ELSE
|
|
NB = MAX( 1, ILAENV( 1, 'DPTTRS', ' ', N, NRHS, -1, -1 ) )
|
|
END IF
|
|
*
|
|
IF( NB.GE.NRHS ) THEN
|
|
CALL DPTTS2( N, NRHS, D, E, B, LDB )
|
|
ELSE
|
|
DO 10 J = 1, NRHS, NB
|
|
JB = MIN( NRHS-J+1, NB )
|
|
CALL DPTTS2( N, JB, D, E, B( 1, J ), LDB )
|
|
10 CONTINUE
|
|
END IF
|
|
*
|
|
RETURN
|
|
*
|
|
* End of DPTTRS
|
|
*
|
|
END
|