SRC/dtptri.f(3)

NAME
SRC/dtptri.f

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.

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 116 of file dtptri.f.

Author

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