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

```SDISNA(l)								 )								 SDISNA(l)

NAME
SDISNA  -  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 SDISNA( JOB, M, N, D, SEP, INFO )

CHARACTER	  JOB

INTEGER	  INFO, M, N

REAL 	  D( * ), SEP( * )

PURPOSE
SDISNA 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

SLAMCH( 'E' ) * ( ANORM / SEP( I ) )

where ANORM = 2-norm(A) = max( abs( D(j) ) ).  SEP(I) is not allowed to be smaller than SLAMCH( 'E' )*ANORM in order to limit the  size	of
the error bound.

SDISNA may also be used to compute error bounds for eigenvectors of the generalized symmetric 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) REAL 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) REAL 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 							 SDISNA(l)```