ddisna.f(3)

NAME
ddisna.f -

SYNOPSIS

  Functions/Subroutines
subroutine ddisna (JOB, M, N, D, SEP, INFO)
DDISNA

Function/Subroutine Documentation

  subroutine ddisna (characterJOB, integerM, integerN, double precision, dimension( * )D, double precision, dimension( * )SEP, integerINFO)

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.

Date:
    November 2011

Definition at line 118 of file ddisna.f.

Author

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