LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ dlaptm()

subroutine dlaptm ( integer  n,
integer  nrhs,
double precision  alpha,
double precision, dimension( * )  d,
double precision, dimension( * )  e,
double precision, dimension( ldx, * )  x,
integer  ldx,
double precision  beta,
double precision, dimension( ldb, * )  b,
integer  ldb 
)

DLAPTM

Purpose:
 DLAPTM 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.
Parameters
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in]NRHS
          NRHS is INTEGER
          The number of right hand sides, i.e., the number of columns
          of the matrices X and B.
[in]ALPHA
          ALPHA is DOUBLE PRECISION
          The scalar alpha.  ALPHA must be 1. or -1.; otherwise,
          it is assumed to be 0.
[in]D
          D is DOUBLE PRECISION array, dimension (N)
          The n diagonal elements of the tridiagonal matrix A.
[in]E
          E is DOUBLE PRECISION array, dimension (N-1)
          The (n-1) subdiagonal or superdiagonal elements of A.
[in]X
          X is DOUBLE PRECISION array, dimension (LDX,NRHS)
          The N by NRHS matrix X.
[in]LDX
          LDX is INTEGER
          The leading dimension of the array X.  LDX >= max(N,1).
[in]BETA
          BETA is DOUBLE PRECISION
          The scalar beta.  BETA must be 0., 1., or -1.; otherwise,
          it is assumed to be 1.
[in,out]B
          B is DOUBLE PRECISION 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.
[in]LDB
          LDB is INTEGER
          The leading dimension of the array B.  LDB >= max(N,1).
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 115 of file dlaptm.f.

116*
117* -- LAPACK test routine --
118* -- LAPACK is a software package provided by Univ. of Tennessee, --
119* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
120*
121* .. Scalar Arguments ..
122 INTEGER LDB, LDX, N, NRHS
123 DOUBLE PRECISION ALPHA, BETA
124* ..
125* .. Array Arguments ..
126 DOUBLE PRECISION B( LDB, * ), D( * ), E( * ), X( LDX, * )
127* ..
128*
129* =====================================================================
130*
131* .. Parameters ..
132 DOUBLE PRECISION ONE, ZERO
133 parameter( one = 1.0d+0, zero = 0.0d+0 )
134* ..
135* .. Local Scalars ..
136 INTEGER I, J
137* ..
138* .. Executable Statements ..
139*
140 IF( n.EQ.0 )
141 $ RETURN
142*
143* Multiply B by BETA if BETA.NE.1.
144*
145 IF( beta.EQ.zero ) THEN
146 DO 20 j = 1, nrhs
147 DO 10 i = 1, n
148 b( i, j ) = zero
149 10 CONTINUE
150 20 CONTINUE
151 ELSE IF( beta.EQ.-one ) THEN
152 DO 40 j = 1, nrhs
153 DO 30 i = 1, n
154 b( i, j ) = -b( i, j )
155 30 CONTINUE
156 40 CONTINUE
157 END IF
158*
159 IF( alpha.EQ.one ) THEN
160*
161* Compute B := B + A*X
162*
163 DO 60 j = 1, nrhs
164 IF( n.EQ.1 ) THEN
165 b( 1, j ) = b( 1, j ) + d( 1 )*x( 1, j )
166 ELSE
167 b( 1, j ) = b( 1, j ) + d( 1 )*x( 1, j ) +
168 $ e( 1 )*x( 2, j )
169 b( n, j ) = b( n, j ) + e( n-1 )*x( n-1, j ) +
170 $ d( n )*x( n, j )
171 DO 50 i = 2, n - 1
172 b( i, j ) = b( i, j ) + e( i-1 )*x( i-1, j ) +
173 $ d( i )*x( i, j ) + e( i )*x( i+1, j )
174 50 CONTINUE
175 END IF
176 60 CONTINUE
177 ELSE IF( alpha.EQ.-one ) THEN
178*
179* Compute B := B - A*X
180*
181 DO 80 j = 1, nrhs
182 IF( n.EQ.1 ) THEN
183 b( 1, j ) = b( 1, j ) - d( 1 )*x( 1, j )
184 ELSE
185 b( 1, j ) = b( 1, j ) - d( 1 )*x( 1, j ) -
186 $ e( 1 )*x( 2, j )
187 b( n, j ) = b( n, j ) - e( n-1 )*x( n-1, j ) -
188 $ d( n )*x( n, j )
189 DO 70 i = 2, n - 1
190 b( i, j ) = b( i, j ) - e( i-1 )*x( i-1, j ) -
191 $ d( i )*x( i, j ) - e( i )*x( i+1, j )
192 70 CONTINUE
193 END IF
194 80 CONTINUE
195 END IF
196 RETURN
197*
198* End of DLAPTM
199*
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