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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( * )



     #include <sunperf.h>

     void ddisna(char job, int m, int n, double *d,
                double *sep, int *info) ;

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  eigen-
     vectors of the generalized symmetric definite eigenproblem.


ARGUMENTS
     JOB       (input) CHARACTER*1
               Specifies for which problem the reciprocal  condi-
               tion 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 singular 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 ille-
               gal value.

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