1CTPTRI(1)                LAPACK routine (version 3.2)                CTPTRI(1)
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NAME

6       CTPTRI  -  computes  the inverse of a complex upper or lower triangular
7       matrix A stored in packed format
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SYNOPSIS

10       SUBROUTINE CTPTRI( UPLO, DIAG, N, AP, INFO )
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12           CHARACTER      DIAG, UPLO
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14           INTEGER        INFO, N
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16           COMPLEX        AP( * )
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PURPOSE

19       CTPTRI computes the inverse of a  complex  upper  or  lower  triangular
20       matrix A stored in packed format.
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ARGUMENTS

23       UPLO    (input) CHARACTER*1
24               = 'U':  A is upper triangular;
25               = 'L':  A is lower triangular.
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27       DIAG    (input) CHARACTER*1
28               = 'N':  A is non-unit triangular;
29               = 'U':  A is unit triangular.
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31       N       (input) INTEGER
32               The order of the matrix A.  N >= 0.
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34       AP      (input/output) COMPLEX array, dimension (N*(N+1)/2)
35               On entry, the upper or lower triangular matrix A, stored colum‐
36               nwise in a linear array.  The j-th column of A is stored in the
37               array  AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j)
38               for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*((2*n-j)/2)  =  A(i,j)
39               for  j<=i<=n.   See  below  for  further details.  On exit, the
40               (triangular) inverse of the original matrix, in the same packed
41               storage format.
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43       INFO    (output) INTEGER
44               = 0:  successful exit
45               < 0:  if INFO = -i, the i-th argument had an illegal value
46               >  0:   if  INFO  =  i, A(i,i) is exactly zero.  The triangular
47               matrix is singular and its inverse can not be computed.
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FURTHER DETAILS

50       A triangular matrix A can be transferred to packed storage using one of
51       the following program segments:
52       UPLO = 'U':                      UPLO = 'L':
53             JC = 1                           JC = 1
54             DO 2 J = 1, N                    DO 2 J = 1, N
55                DO 1 I = 1, J                    DO 1 I = J, N
56                   AP(JC+I-1) = A(I,J)              AP(JC+I-J) = A(I,J)
57           1    CONTINUE                    1    CONTINUE
58                JC = JC + J                      JC = JC + N - J + 1
59           2 CONTINUE                       2 CONTINUE
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63 LAPACK routine (version 3.2)    November 2008                       CTPTRI(1)