# ctptri.f man page

ctptri.f

## Synopsis

### Functions/Subroutines

subroutine ctptri (UPLO, DIAG, N, AP, INFO)
CTPTRI

## Function/Subroutine Documentation

### subroutine ctptri (character UPLO, character DIAG, integer N, complex, dimension( * ) AP, integer INFO)

CTPTRI

Purpose:

``` CTPTRI computes the inverse of a complex 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 COMPLEX 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

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 ctptri.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Tue Nov 14 2017 Version 3.8.0 LAPACK