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## slas2()

subroutine slas2 | ( | real | f,
|  | real | g,
|  | real | h,
|  | real | ssmin,
|  | real | ssmax )

SLAS2 computes singular values of a 2-by-2 triangular matrix.

Download SLAS2 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

      !>
      !> SLAS2  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 REAL
      !>          The (1,1) element of the 2-by-2 matrix.
      !>

  [in]

  G

      !>          G is REAL
      !>          The (1,2) element of the 2-by-2 matrix.
      !>

  [in]

  H

      !>          H is REAL
      !>          The (2,2) element of the 2-by-2 matrix.
      !>

  [out]

  SSMIN

      !>          SSMIN is REAL
      !>          The smaller singular value.
      !>

  [out]

  SSMAX

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