# dtptri.f - Man Page

## Synopsis

### Functions/Subroutines

subroutine **dtptri** (UPLO, DIAG, **N**, AP, INFO)**DTPTRI**

## Function/Subroutine Documentation

### subroutine dtptri (character UPLO, character DIAG, integer N, double precision, dimension( * ) AP, integer INFO)

**DTPTRI**

**Purpose:**

DTPTRI 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 DOUBLE PRECISION 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.

**Date:**December 2016

**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 119 of file dtptri.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Tue Nov 14 2017 Version 3.8.0 LAPACK