dlas2()

subroutine dlas2	(	double precision	F,
		double precision	G,
		double precision	H,
		double precision	SSMIN,
		double precision	SSMAX
	)

DLAS2 computes singular values of a 2-by-2 triangular matrix.

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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.

Parameters

[in]	F	F is DOUBLE PRECISION The (1,1) element of the 2-by-2 matrix.
[in]	G	G is DOUBLE PRECISION The (1,2) element of the 2-by-2 matrix.
[in]	H	H is DOUBLE PRECISION The (2,2) element of the 2-by-2 matrix.
[out]	SSMIN	SSMIN is DOUBLE PRECISION The smaller singular value.
[out]	SSMAX	SSMAX is DOUBLE PRECISION The larger singular value.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

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.