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*> \brief \b SLAPTM
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
* Definition:
* ===========
*
* SUBROUTINE SLAPTM( N, NRHS, ALPHA, D, E, X, LDX, BETA, B, LDB )
*
* .. Scalar Arguments ..
* INTEGER LDB, LDX, N, NRHS
* REAL ALPHA, BETA
* ..
* .. Array Arguments ..
* REAL B( LDB, * ), D( * ), E( * ), X( LDX, * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> SLAPTM multiplies an N by NRHS matrix X by a symmetric tridiagonal
*> matrix A and stores the result in a matrix B. The operation has the
*> form
*>
*> B := alpha * A * X + beta * B
*>
*> where alpha may be either 1. or -1. and beta may be 0., 1., or -1.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The order of the 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 matrices X and B.
*> \endverbatim
*>
*> \param[in] ALPHA
*> \verbatim
*> ALPHA is REAL
*> The scalar alpha. ALPHA must be 1. or -1.; otherwise,
*> it is assumed to be 0.
*> \endverbatim
*>
*> \param[in] D
*> \verbatim
*> D is REAL array, dimension (N)
*> The n diagonal elements of the tridiagonal matrix A.
*> \endverbatim
*>
*> \param[in] E
*> \verbatim
*> E is REAL array, dimension (N-1)
*> The (n-1) subdiagonal or superdiagonal elements of A.
*> \endverbatim
*>
*> \param[in] X
*> \verbatim
*> X is REAL array, dimension (LDX,NRHS)
*> The N by NRHS matrix X.
*> \endverbatim
*>
*> \param[in] LDX
*> \verbatim
*> LDX is INTEGER
*> The leading dimension of the array X. LDX >= max(N,1).
*> \endverbatim
*>
*> \param[in] BETA
*> \verbatim
*> BETA is REAL
*> The scalar beta. BETA must be 0., 1., or -1.; otherwise,
*> it is assumed to be 1.
*> \endverbatim
*>
*> \param[in,out] B
*> \verbatim
*> B is REAL array, dimension (LDB,NRHS)
*> On entry, the N by NRHS matrix B.
*> On exit, B is overwritten by the matrix expression
*> B := alpha * A * X + beta * B.
*> \endverbatim
*>
*> \param[in] LDB
*> \verbatim
*> LDB is INTEGER
*> The leading dimension of the array B. LDB >= max(N,1).
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup single_lin
*
* =====================================================================
SUBROUTINE SLAPTM( N, NRHS, ALPHA, D, E, X, LDX, BETA, B, LDB )
*
* -- LAPACK test routine --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
* .. Scalar Arguments ..
INTEGER LDB, LDX, N, NRHS
REAL ALPHA, BETA
* ..
* .. Array Arguments ..
REAL B( LDB, * ), D( * ), E( * ), X( LDX, * )
* ..
*
* =====================================================================
*
* .. Parameters ..
REAL ONE, ZERO
PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
* ..
* .. Local Scalars ..
INTEGER I, J
* ..
* .. Executable Statements ..
*
IF( N.EQ.0 )
$ RETURN
*
* Multiply B by BETA if BETA.NE.1.
*
IF( BETA.EQ.ZERO ) THEN
DO 20 J = 1, NRHS
DO 10 I = 1, N
B( I, J ) = ZERO
10 CONTINUE
20 CONTINUE
ELSE IF( BETA.EQ.-ONE ) THEN
DO 40 J = 1, NRHS
DO 30 I = 1, N
B( I, J ) = -B( I, J )
30 CONTINUE
40 CONTINUE
END IF
*
IF( ALPHA.EQ.ONE ) THEN
*
* Compute B := B + A*X
*
DO 60 J = 1, NRHS
IF( N.EQ.1 ) THEN
B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J )
ELSE
B( 1, J ) = B( 1, J ) + D( 1 )*X( 1, J ) +
$ E( 1 )*X( 2, J )
B( N, J ) = B( N, J ) + E( N-1 )*X( N-1, J ) +
$ D( N )*X( N, J )
DO 50 I = 2, N - 1
B( I, J ) = B( I, J ) + E( I-1 )*X( I-1, J ) +
$ D( I )*X( I, J ) + E( I )*X( I+1, J )
50 CONTINUE
END IF
60 CONTINUE
ELSE IF( ALPHA.EQ.-ONE ) THEN
*
* Compute B := B - A*X
*
DO 80 J = 1, NRHS
IF( N.EQ.1 ) THEN
B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J )
ELSE
B( 1, J ) = B( 1, J ) - D( 1 )*X( 1, J ) -
$ E( 1 )*X( 2, J )
B( N, J ) = B( N, J ) - E( N-1 )*X( N-1, J ) -
$ D( N )*X( N, J )
DO 70 I = 2, N - 1
B( I, J ) = B( I, J ) - E( I-1 )*X( I-1, J ) -
$ D( I )*X( I, J ) - E( I )*X( I+1, J )
70 CONTINUE
END IF
80 CONTINUE
END IF
RETURN
*
* End of SLAPTM
*
END
|
