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NAME
     slaev2 - compute the eigendecomposition  of  a  2-by-2  sym-
     metric matrix  [ A B ]  [ B C ]

SYNOPSIS
     SUBROUTINE SLAEV2( A, B, C, RT1, RT2, CS1, SN1 )

     REAL A, B, C, CS1, RT1, RT2, SN1



     #include <sunperf.h>

     void slaev2(float a, float b, float  c,  float  *rt1,  float
               *rt2, float *cs1, float *sn1) ;

PURPOSE
     SLAEV2 computes the eigendecomposition of a 2-by-2 symmetric
     matrix

        [  A   B  ]
        [  B   C  ].

     On return, RT1 is the eigenvalue of larger  absolute  value,
     RT2  is  the  eigenvalue  of  smaller  absolute  value,  and
     (CS1,SN1) is the unit right eigenvector for RT1, giving  the
     decomposition

        [ CS1  SN1 ] [  A   B  ] [ CS1 -SN1 ]  =  [ RT1  0  ]
        [-SN1  CS1 ] [  B   C  ] [ SN1  CS1 ]     [  0  RT2 ].


ARGUMENTS
     A         (input) REAL
               The (1,1) element of the 2-by-2 matrix.

     B         (input) REAL
               The (1,2) element and the conjugate of  the  (2,1)
               element of the 2-by-2 matrix.

     C         (input) REAL
               The (2,2) element of the 2-by-2 matrix.

     RT1       (output) REAL
               The eigenvalue of larger absolute value.

     RT2       (output) REAL
               The eigenvalue of smaller absolute value.

     CS1       (output) REAL
               SN1     (output) REAL The vector (CS1, SN1)  is  a
               unit right eigenvector for RT1.

FURTHER DETAILS
     RT1 is accurate to a few ulps barring over/underflow.

     RT2 may be inaccurate if there is  massive  cancellation  in
     the  determinant  A*C-B*B;  higher  precision  or  correctly
     rounded or correctly truncated arithmetic would be needed to
     compute RT2 accurately in all cases.

     CS1  and  SN1  are  accurate   to   a   few   ulps   barring
     over/underflow.

     Overflow is possible only if RT1 is within a factor of 5  of
     overflow.   Underflow  is harmless if the input data is 0 or
     exceeds
        underflow_threshold / macheps.

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