# dlagtm.f man page

dlagtm.f —

## Synopsis

### Functions/Subroutines

subroutinedlagtm(TRANS, N, NRHS, ALPHA, DL, D, DU, X, LDX, BETA, B, LDB)DLAGTMperforms 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 (characterTRANS, integerN, integerNRHS, double precisionALPHA, double precision, dimension( * )DL, double precision, dimension( * )D, double precision, dimension( * )DU, double precision, dimension( ldx, * )X, integerLDX, double precisionBETA, double precision, dimension( ldb, * )B, integerLDB)

**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

Univ. of Colorado Denver

NAG Ltd.

**Date:**

September 2012

Definition at line 145 of file dlagtm.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

dlagtm(3) is an alias of dlagtm.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK