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RedHat 9 (Linux i386) - man page for ddisna (redhat section l)

DDISNA(l)					)					DDISNA(l)

NAME
       DDISNA - compute 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

SYNOPSIS
       SUBROUTINE DDISNA( JOB, M, N, D, SEP, INFO )

	   CHARACTER	  JOB

	   INTEGER	  INFO, M, N

	   DOUBLE	  PRECISION D( * ), SEP( * )

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  sym-
       metric definite eigenproblem.

ARGUMENTS
       JOB     (input) 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       (input) INTEGER
	       The number of rows of the matrix. M >= 0.

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

       D       (input) DOUBLE PRECISION array, dimension (M) if JOB = 'E'
	       dimension (min(M,N)) if JOB = 'L' or 'R' The eigenvalues (if JOB = 'E') or  singu-
	       lar values (if JOB = order. If singular values, they must be non-negative.

       SEP     (output) 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    (output) INTEGER
	       = 0:  successful exit.
	       < 0:  if INFO = -i, the i-th argument had an illegal value.

LAPACK version 3.0			   15 June 2000 				DDISNA(l)


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