---
name: "strtri"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/strtri/3lapack"
---

# strtri(3lapack)

computes the inverse of a real upper or lower triangular matrix A

## NAME

STRTRI - computes the inverse of a real upper or lower triangular matrix A

## SYNOPSIS

- SUBROUTINE STRTRI(

  UPLO, DIAG, N, A, LDA, INFO )

- CHARACTER

  DIAG, UPLO

- INTEGER

  INFO, LDA, N

- REAL

  A( LDA, \* )

## PURPOSE

STRTRI computes the inverse of a real upper or lower triangular matrix A. This is the Level 3 BLAS version of the algorithm.\

## ARGUMENTS

- UPLO (input) CHARACTER\*1

  \= 'U':  A is upper triangular;\
   \= 'L':  A is lower triangular.

- DIAG (input) CHARACTER\*1

  \= 'N':  A is non-unit triangular;\
   \= 'U':  A is unit triangular.

- N (input) INTEGER

  The order of the matrix A.  N \>= 0.

- A (input/output) 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 (input) INTEGER

  The leading dimension of the array A.  LDA \>= max(1,N).

- INFO (output) INTEGER

  \= 0: successful exit\
   \< 0: if INFO = -i, the i-th argument had an illegal value\
   \> 0: if INFO = i, A(i,i) is exactly zero.  The triangular matrix is singular and its inverse can not be computed.