redhat man page for dlae2

DLAE2(l)								 )								  DLAE2(l)

NAME
       DLAE2 - compute the eigenvalues of a 2-by-2 symmetric matrix [ A B ] [ B C ]

SYNOPSIS
       SUBROUTINE DLAE2( A, B, C, RT1, RT2 )

	   DOUBLE	 PRECISION A, B, C, RT1, RT2

PURPOSE
       DLAE2 computes the eigenvalues of a 2-by-2 symmetric matrix [ A B ] [ B C ]. On return, RT1 is the eigenvalue of larger absolute value, and
       RT2 is the eigenvalue of smaller absolute value.

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

       B       (input) DOUBLE PRECISION
	       The (1,2) and (2,1) elements of the 2-by-2 matrix.

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

       RT1     (output) DOUBLE PRECISION
	       The eigenvalue of larger absolute value.

       RT2     (output) DOUBLE PRECISION
	       The eigenvalue of smaller absolute value.

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 trun-
       cated arithmetic would be needed to compute RT2 accurately in all cases.

       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.

LAPACK version 3.0						   15 June 2000 							  DLAE2(l)