---
name: "zlagtm"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/zlagtm.f"
---

# zlagtm(3)

Part of [zlagtm.f(3)](/zlagtm.f/3.md).

## NAME

SRC/zlagtm.f

## SYNOPSIS

### Functions/Subroutines

subroutine **zlagtm** (trans, n, nrhs, alpha, dl, d, du, x, ldx, beta, b, ldb)\
 **ZLAGTM** 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 zlagtm (character trans, integer n, integer nrhs, double precision alpha, complex\*16, dimension( \* ) dl, complex\*16, dimension( \* ) d, complex\*16, dimension( \* ) du, complex\*16, dimension( ldx, \* ) x, integer ldx, double precision beta, complex\*16, dimension( ldb, \* ) b, integer ldb)

**ZLAGTM** 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:**

```
!>
!> ZLAGTM performs a matrix-matrix 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**T * X + beta * B
!>          = 'C':  Conjugate transpose, B := alpha * A**H * X + beta * B
!>
```

*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 COMPLEX*16 array, dimension (N-1)
!>          The (n-1) sub-diagonal elements of T.
!>
```

*D*

```
!>          D is COMPLEX*16 array, dimension (N)
!>          The diagonal elements of T.
!>
```

*DU*

```
!>          DU is COMPLEX*16 array, dimension (N-1)
!>          The (n-1) super-diagonal elements of T.
!>
```

*X*

```
!>          X is COMPLEX*16 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 COMPLEX*16 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.

Definition at line **143** of file **zlagtm.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.