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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