---
name: "trti2"
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/trti2"
---

# trti2(3)

trti2: triangular inverse, level 2

## NAME

trti2 - trti2: triangular inverse, level 2

## SYNOPSIS

### Functions

subroutine **ctrti2** (uplo, diag, n, a, lda, info)\
 **CTRTI2** computes the inverse of a triangular matrix (unblocked algorithm).  subroutine **dtrti2** (uplo, diag, n, a, lda, info)\
 **DTRTI2** computes the inverse of a triangular matrix (unblocked algorithm).  subroutine **strti2** (uplo, diag, n, a, lda, info)\
 **STRTI2** computes the inverse of a triangular matrix (unblocked algorithm).  subroutine **ztrti2** (uplo, diag, n, a, lda, info)\
 **ZTRTI2** computes the inverse of a triangular matrix (unblocked algorithm).

## Detailed Description

## Function Documentation

### subroutine ctrti2 (character uplo, character diag, integer n, complex, dimension( lda, \* ) a, integer lda, integer info)

**CTRTI2** computes the inverse of a triangular matrix (unblocked algorithm).

**Purpose:**

```
!>
!> CTRTI2 computes the inverse of a complex upper or lower triangular
!> matrix.
!>
!> This is the Level 2 BLAS version of the algorithm.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          Specifies whether the matrix A is upper or lower triangular.
!>          = 'U':  Upper triangular
!>          = 'L':  Lower triangular
!>
```

*DIAG*

```
!>          DIAG is CHARACTER*1
!>          Specifies whether or not the matrix A is unit triangular.
!>          = 'N':  Non-unit triangular
!>          = 'U':  Unit triangular
!>
```

*N*

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

*A*

```
!>          A is COMPLEX array, dimension (LDA,N)
!>          On entry, the triangular matrix A.  If UPLO = 'U', the
!>          leading n by n upper triangular part of the array A contains
!>          the upper triangular matrix, and the strictly lower
!>          triangular part of A is not referenced.  If UPLO = 'L', the
!>          leading n by n lower triangular part of the array A contains
!>          the lower triangular matrix, and the strictly upper
!>          triangular part of A is not referenced.  If DIAG = 'U', the
!>          diagonal elements of A are also not referenced and are
!>          assumed to be 1.
!>
!>          On exit, the (triangular) inverse of the original matrix, in
!>          the same storage format.
!>
```

*LDA*

```
!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max(1,N).
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -k, the k-th argument had an illegal value
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **109** of file **ctrti2.f**.

### subroutine dtrti2 (character uplo, character diag, integer n, double precision, dimension( lda, \* ) a, integer lda, integer info)

**DTRTI2** computes the inverse of a triangular matrix (unblocked algorithm).

**Purpose:**

```
!>
!> DTRTI2 computes the inverse of a real upper or lower triangular
!> matrix.
!>
!> This is the Level 2 BLAS version of the algorithm.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          Specifies whether the matrix A is upper or lower triangular.
!>          = 'U':  Upper triangular
!>          = 'L':  Lower triangular
!>
```

*DIAG*

```
!>          DIAG is CHARACTER*1
!>          Specifies whether or not the matrix A is unit triangular.
!>          = 'N':  Non-unit triangular
!>          = 'U':  Unit triangular
!>
```

*N*

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

*A*

```
!>          A is DOUBLE PRECISION array, dimension (LDA,N)
!>          On entry, the triangular matrix A.  If UPLO = 'U', the
!>          leading n by n upper triangular part of the array A contains
!>          the upper triangular matrix, and the strictly lower
!>          triangular part of A is not referenced.  If UPLO = 'L', the
!>          leading n by n lower triangular part of the array A contains
!>          the lower triangular matrix, and the strictly upper
!>          triangular part of A is not referenced.  If DIAG = 'U', the
!>          diagonal elements of A are also not referenced and are
!>          assumed to be 1.
!>
!>          On exit, the (triangular) inverse of the original matrix, in
!>          the same storage format.
!>
```

*LDA*

```
!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max(1,N).
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -k, the k-th argument had an illegal value
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **109** of file **dtrti2.f**.

### subroutine strti2 (character uplo, character diag, integer n, real, dimension( lda, \* ) a, integer lda, integer info)

**STRTI2** computes the inverse of a triangular matrix (unblocked algorithm).

**Purpose:**

```
!>
!> STRTI2 computes the inverse of a real upper or lower triangular
!> matrix.
!>
!> This is the Level 2 BLAS version of the algorithm.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          Specifies whether the matrix A is upper or lower triangular.
!>          = 'U':  Upper triangular
!>          = 'L':  Lower triangular
!>
```

*DIAG*

```
!>          DIAG is CHARACTER*1
!>          Specifies whether or not the matrix A is unit triangular.
!>          = 'N':  Non-unit triangular
!>          = 'U':  Unit triangular
!>
```

*N*

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

*A*

```
!>          A is REAL array, dimension (LDA,N)
!>          On entry, the triangular matrix A.  If UPLO = 'U', the
!>          leading n by n upper triangular part of the array A contains
!>          the upper triangular matrix, and the strictly lower
!>          triangular part of A is not referenced.  If UPLO = 'L', the
!>          leading n by n lower triangular part of the array A contains
!>          the lower triangular matrix, and the strictly upper
!>          triangular part of A is not referenced.  If DIAG = 'U', the
!>          diagonal elements of A are also not referenced and are
!>          assumed to be 1.
!>
!>          On exit, the (triangular) inverse of the original matrix, in
!>          the same storage format.
!>
```

*LDA*

```
!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max(1,N).
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -k, the k-th argument had an illegal value
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **109** of file **strti2.f**.

### subroutine ztrti2 (character uplo, character diag, integer n, complex\*16, dimension( lda, \* ) a, integer lda, integer info)

**ZTRTI2** computes the inverse of a triangular matrix (unblocked algorithm).

**Purpose:**

```
!>
!> ZTRTI2 computes the inverse of a complex upper or lower triangular
!> matrix.
!>
!> This is the Level 2 BLAS version of the algorithm.
!>
```

**Parameters**

*UPLO*

```
!>          UPLO is CHARACTER*1
!>          Specifies whether the matrix A is upper or lower triangular.
!>          = 'U':  Upper triangular
!>          = 'L':  Lower triangular
!>
```

*DIAG*

```
!>          DIAG is CHARACTER*1
!>          Specifies whether or not the matrix A is unit triangular.
!>          = 'N':  Non-unit triangular
!>          = 'U':  Unit triangular
!>
```

*N*

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

*A*

```
!>          A is COMPLEX*16 array, dimension (LDA,N)
!>          On entry, the triangular matrix A.  If UPLO = 'U', the
!>          leading n by n upper triangular part of the array A contains
!>          the upper triangular matrix, and the strictly lower
!>          triangular part of A is not referenced.  If UPLO = 'L', the
!>          leading n by n lower triangular part of the array A contains
!>          the lower triangular matrix, and the strictly upper
!>          triangular part of A is not referenced.  If DIAG = 'U', the
!>          diagonal elements of A are also not referenced and are
!>          assumed to be 1.
!>
!>          On exit, the (triangular) inverse of the original matrix, in
!>          the same storage format.
!>
```

*LDA*

```
!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max(1,N).
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -k, the k-th argument had an illegal value
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **109** of file **ztrti2.f**.

## Author

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