# dlagtm.f

Section: LAPACK (3)
Updated: Tue Nov 14 2017
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dlagtm.f

## SYNOPSIS

### Functions/Subroutines

subroutine dlagtm (TRANS, N, NRHS, ALPHA, DL, D, DU, X, LDX, BETA, B, LDB)
DLAGTM performs a matrix-matrix product of the form C = αAB+βC, where A is a tridiagonal matrix, B and C are rectangular matrices, and α and β are scalars, which may be 0, 1, or -1.

## Function/Subroutine Documentation

### subroutine dlagtm (character TRANS, integer N, integer NRHS, double precision ALPHA, double precision, dimension( * ) DL, double precision, dimension( * ) D, double precision, dimension( * ) DU, double precision, dimension( ldx, * ) X, integer LDX, double precision BETA, double precision, dimension( ldb, * ) B, integer LDB)

DLAGTM performs a matrix-matrix product of the form C = αAB+βC, where A is a tridiagonal matrix, B and C are rectangular matrices, and α and β are scalars, which may be 0, 1, or -1.

Purpose:

``` DLAGTM performs 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.
```

Parameters:

TRANS

```          TRANS is CHARACTER*1
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

```          N is INTEGER
The order of the matrix A.  N >= 0.
```

NRHS

```          NRHS is INTEGER
The number of right hand sides, i.e., the number of columns
of the matrices X and B.
```

ALPHA

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

DL

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

D

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

DU

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

X

```          X is DOUBLE PRECISION array, dimension (LDX,NRHS)
The N by NRHS matrix X.
```

LDX

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

BETA

```          BETA is DOUBLE PRECISION
The scalar beta.  BETA must be 0., 1., or -1.; otherwise,
it is assumed to be 1.
```

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.
```

LDB

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

Author:

Univ. of Tennessee

Univ. of California Berkeley