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# dlagtm

```
NAME
DLAGTM - perform a matrix-vector product of the form   B :=
alpha * A * X + beta * B  where A is a tridiagonal matrix of
order N, B and X are N by NRHS matrices, and alpha and beta
are real scalars, each of which may be 0., 1., or -1

SYNOPSIS
SUBROUTINE DLAGTM( TRANS, N, NRHS, ALPHA, DL, D, DU, X, LDX,
BETA, B, LDB )

CHARACTER      TRANS

INTEGER        LDB, LDX, N, NRHS

DOUBLE         PRECISION ALPHA, BETA

DOUBLE         PRECISION B( LDB, * ), D( * ), DL( * ),
DU( * ), X( LDX, * )

PURPOSE
DLAGTM performs a matrix-vector product of the form

ARGUMENTS
TRANS   (input) CHARACTER
Specifies the operation applied to A.  = 'N':  No
transpose, B := alpha * A * X + beta * B
= 'T':  Transpose,    B := alpha * A'* X + beta * B
= 'C':  Conjugate transpose = Transpose

N       (input) INTEGER
The order of the matrix A.  N >= 0.

NRHS    (input) INTEGER
The number of right hand sides, i.e., the number of
columns of the matrices X and B.

ALPHA   (input) DOUBLE PRECISION
The scalar alpha.  ALPHA must be 0., 1., or -1.;
otherwise, it is assumed to be 0.

DL      (input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) sub-diagonal elements of T.

D       (input) DOUBLE PRECISION array, dimension (N)
The diagonal elements of T.

DU      (input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) super-diagonal elements of T.

X       (input) DOUBLE PRECISION array, dimension (LDX,NRHS)
The N by NRHS matrix X.  LDX     (input) INTEGER The

leading dimension of the array X.  LDX >= max(N,1).

BETA    (input) DOUBLE PRECISION
The scalar beta.  BETA must be 0., 1., or -1.; oth-
erwise, it is assumed to be 1.

(LDB,NRHS)
B       (input/output) DOUBLE PRECISION array, dimension
On entry, the N by NRHS matrix B.  On exit, B is
overwritten by the matrix expression B := alpha * A
* X + beta * B.

LDB     (input) INTEGER
The leading dimension of the array B.  LDB >=
max(N,1).
```