SRC/ddisna.f(3)

NAME
SRC/ddisna.f

SYNOPSIS

  Functions/Subroutines
subroutine ddisna (job, m, n, d, sep, info)
DDISNA

Function/Subroutine Documentation

  subroutine ddisna (character job, integer m, integer n, double precision, dimension( * ) d, double precision, dimension( * ) sep, integer info)

DDISNA

Purpose:

    !>
    !> DDISNA computes the reciprocal condition numbers for the eigenvectors
    !> of a real symmetric or complex Hermitian matrix or for the left or
    !> right singular vectors of a general m-by-n matrix. The reciprocal
    !> condition number is the 'gap' between the corresponding eigenvalue or
    !> singular value and the nearest other one.
    !>
    !> The bound on the error, measured by angle in radians, in the I-th
    !> computed vector is given by
    !>
    !>        DLAMCH( 'E' ) * ( ANORM / SEP( I ) )
    !>
    !> where ANORM = 2-norm(A) = max( abs( D(j) ) ).  SEP(I) is not allowed
    !> to be smaller than DLAMCH( 'E' )*ANORM in order to limit the size of
    !> the error bound.
    !>
    !> DDISNA may also be used to compute error bounds for eigenvectors of
    !> the generalized symmetric definite eigenproblem.
    !>

Parameters
    JOB

    !>          JOB is CHARACTER*1
    !>          Specifies for which problem the reciprocal condition numbers
    !>          should be computed:
    !>          = 'E':  the eigenvectors of a symmetric/Hermitian matrix;
    !>          = 'L':  the left singular vectors of a general matrix;
    !>          = 'R':  the right singular vectors of a general matrix.
    !>

    M

    !>          M is INTEGER
    !>          The number of rows of the matrix. M >= 0.
    !>

    N

    !>          N is INTEGER
    !>          If JOB = 'L' or 'R', the number of columns of the matrix,
    !>          in which case N >= 0. Ignored if JOB = 'E'.
    !>

    D

    !>          D is DOUBLE PRECISION array, dimension (M) if JOB = 'E'
    !>                              dimension (min(M,N)) if JOB = 'L' or 'R'
    !>          The eigenvalues (if JOB = 'E') or singular values (if JOB =
    !>          'L' or 'R') of the matrix, in either increasing or decreasing
    !>          order. If singular values, they must be non-negative.
    !>

    SEP

    !>          SEP is DOUBLE PRECISION array, dimension (M) if JOB = 'E'
    !>                               dimension (min(M,N)) if JOB = 'L' or 'R'
    !>          The reciprocal condition numbers of the vectors.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit.
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 116 of file ddisna.f.

Author

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