# dlagtm.f man page

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

Univ. of Colorado Denver

NAG Ltd.

**Date:**December 2016

Definition at line 147 of file dlagtm.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dlagtm(3) is an alias of dlagtm.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK