NAME

       dlaev2.f -

SYNOPSIS

   Functions/Subroutines
       subroutine dlaev2 (A, B, C, RT1, RT2, CS1, SN1)
           DLAEV2 computes the eigenvalues and eigenvectors of a 2-by-2 symmetric/Hermitian
           matrix.

Function/Subroutine Documentation

   subroutine dlaev2 (double precisionA, double precisionB, double precisionC, double
       precisionRT1, double precisionRT2, double precisionCS1, double precisionSN1)
       DLAEV2 computes the eigenvalues and eigenvectors of a 2-by-2 symmetric/Hermitian matrix.

       Purpose:

            DLAEV2 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 ].

       Parameters:
           A

                     A is DOUBLE PRECISION
                     The (1,1) element of the 2-by-2 matrix.

           B

                     B is DOUBLE PRECISION
                     The (1,2) element and the conjugate of the (2,1) element of
                     the 2-by-2 matrix.

           C

                     C is DOUBLE PRECISION
                     The (2,2) element of the 2-by-2 matrix.

           RT1

                     RT1 is DOUBLE PRECISION
                     The eigenvalue of larger absolute value.

           RT2

                     RT2 is DOUBLE PRECISION
                     The eigenvalue of smaller absolute value.

           CS1

                     CS1 is DOUBLE PRECISION

           SN1

                     SN1 is DOUBLE PRECISION
                     The vector (CS1, SN1) is a unit right eigenvector for RT1.

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           September 2012

       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.

       Definition at line 121 of file dlaev2.f.

Author

       Generated automatically by Doxygen for LAPACK from the source code.