CTPTRI - compute the inverse of a complex upper or lower
triangular matrix A stored in packed format
SYNOPSIS
SUBROUTINE CTPTRI( UPLO, DIAG, N, AP, INFO )
CHARACTER DIAG, UPLO
INTEGER INFO, N
COMPLEX AP( * )
PURPOSE
CTPTRI computes the inverse of a complex upper or lower
triangular matrix A stored in packed format.
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.
AP (input/output) 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 for
mat.
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille
gal value
> 0: if INFO = i, A(i,i) is exactly zero. The
triangular matrix is singular and its inverse can
not be computed.
FURTHER DETAILS
A triangular matrix A can be transferred to packed storage
using one of the following program segments:
UPLO = 'U': UPLO = 'L':
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
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