DLAS2(3)       LAPACK routine of NEC Numeric Library Collection       DLAS2(3)



NAME
       DLAS2

SYNOPSIS
       SUBROUTINE DLAS2 (F, G, H, SSMIN, SSMAX)



PURPOSE
            DLAS2  computes the singular values of the 2-by-2 matrix
               [  F   G  ]
               [  0   H  ].
            On return, SSMIN is the smaller singular value and SSMAX is the
            larger singular value.




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

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

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

           SSMIN     (output)
                     SSMIN is DOUBLE PRECISION
                     The smaller singular value.

           SSMAX     (output)
                     SSMAX is DOUBLE PRECISION
                     The larger singular value.






FURTHER DETAILS
             Barring over/underflow, all output quantities are correct to within
             a few units in the last place (ulps), even in the absence of a guard
             digit in addition/subtraction.

             In IEEE arithmetic, the code works correctly if one matrix element is
             infinite.

             Overflow will not occur unless the largest singular value itself
             overflows, or is within a few ulps of overflow. (On machines with
             partial overflow, like the Cray, overflow may occur if the largest
             singular value is within a factor of 2 of overflow.)

             Underflow is harmless if underflow is gradual. Otherwise, results
             may correspond to a matrix modified by perturbations of size near
             the underflow threshold.



LAPACK routine                  31 October 2017                       DLAS2(3)