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## ctptri()

subroutine ctptri | ( | character | uplo,
|  | character | diag,
|  | integer | n,
|  | complex, dimension( * ) | ap,
|  | integer | info )

CTPTRI

Download CTPTRI + dependencies [TGZ] [ZIP] [TXT]

Purpose:

      !>
      !> CTPTRI computes the inverse of a complex upper or lower triangular
      !> matrix A stored in packed format.
      !>

Parameters

  [in]

  UPLO

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

  [in]

  DIAG

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

  [in]

  N

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

  [in,out]

  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.
      !>

  [out]

  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
      !>