claesy.f3

!>
!> CLAESY computes the eigendecomposition of a 2-by-2 symmetric matrix
!>    ( ( A, B );( B, C ) )
!> provided the norm of the matrix of eigenvectors is larger than
!> some threshold value.
!>
!> RT1 is the eigenvalue of larger absolute value, and RT2 of
!> smaller absolute value.  If the eigenvectors are computed, then
!> on return ( CS1, SN1 ) is the unit eigenvector for RT1, hence
!>
!> [  CS1     SN1   ] . [ A  B ] . [ CS1    -SN1   ] = [ RT1  0  ]
!> [ -SN1     CS1   ]   [ B  C ]   [ SN1     CS1   ]   [  0  RT2 ]
!> 

A

!>          A is COMPLEX
!>          The ( 1, 1 ) element of input matrix.
!> 

B

!>          B is COMPLEX
!>          The ( 1, 2 ) element of input matrix.  The ( 2, 1 ) element
!>          is also given by B, since the 2-by-2 matrix is symmetric.
!> 

C

!>          C is COMPLEX
!>          The ( 2, 2 ) element of input matrix.
!> 

RT1

!>          RT1 is COMPLEX
!>          The eigenvalue of larger modulus.
!> 

RT2

!>          RT2 is COMPLEX
!>          The eigenvalue of smaller modulus.
!> 

EVSCAL

!>          EVSCAL is COMPLEX
!>          The complex value by which the eigenvector matrix was scaled
!>          to make it orthonormal.  If EVSCAL is zero, the eigenvectors
!>          were not computed.  This means one of two things:  the 2-by-2
!>          matrix could not be diagonalized, or the norm of the matrix
!>          of eigenvectors before scaling was larger than the threshold
!>          value THRESH (set below).
!> 

CS1

!>          CS1 is COMPLEX
!> 

SN1

!>          SN1 is COMPLEX
!>          If EVSCAL .NE. 0,  ( CS1, SN1 ) is the unit right eigenvector
!>          for RT1.
!> 

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