*> \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. * *> \date December 2016 * *> \ingroup single_lin * * ===================================================================== SUBROUTINE SLAPTM( N, NRHS, ALPHA, D, E, X, LDX, BETA, B, LDB ) * * -- LAPACK test routine (version 3.7.0) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * December 2016 * * .. 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