# stptri.f - Man Page

SRC/stptri.f

## Synopsis

### Functions/Subroutines

subroutine **stptri** (uplo, diag, n, ap, info)**STPTRI**

## Function/Subroutine Documentation

### subroutine stptri (character uplo, character diag, integer n, real, dimension( * ) ap, integer info)

**STPTRI**

**Purpose:**

STPTRI computes the inverse of a real upper or lower triangular matrix A stored in packed format.

**Parameters***UPLO*UPLO is CHARACTER*1 = 'U': A is upper triangular; = 'L': A is lower triangular.

*DIAG*DIAG is CHARACTER*1 = 'N': A is non-unit triangular; = 'U': A is unit triangular.

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

*AP*AP is REAL array, dimension (N*(N+1)/2) On entry, the upper or lower triangular matrix A, stored columnwise in a linear array. The j-th column of A is stored in the array AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*((2*n-j)/2) = A(i,j) for j<=i<=n. See below for further details. On exit, the (triangular) inverse of the original matrix, in the same packed storage format.

*INFO*INFO is 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.

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Further Details:**

A triangular matrix A can be transferred to packed storage using one of the following program segments: UPLO = 'U': UPLO = 'L': JC = 1 JC = 1 DO 2 J = 1, N DO 2 J = 1, N DO 1 I = 1, J DO 1 I = J, N AP(JC+I-1) = A(I,J) AP(JC+I-J) = A(I,J) 1 CONTINUE 1 CONTINUE JC = JC + J JC = JC + N - J + 1 2 CONTINUE 2 CONTINUE

Definition at line **116** of file **stptri.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK