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dlas2 examples
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Man Page Details
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NAME
       DLAS2 - the singular values of the 2-by-2 matrix  [ F G ]  [ 0 H ]

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

           DOUBLE        PRECISION F, G, H, SSMAX, SSMIN

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

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

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

       SSMIN   (output) DOUBLE PRECISION
               The smaller singular value.

       SSMAX   (output) 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 over-
       flows, 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.

