dlas2.f (3)

Functions/Subroutines

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

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

subroutine dlas2 (double precisionF, double precisionG, double precisionH, double precisionSSMIN, double precisionSSMAX)

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

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:

F

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

G

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

H

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

SSMIN

          SSMIN is DOUBLE PRECISION
          The smaller singular value.

SSMAX

          SSMAX is DOUBLE PRECISION
          The larger singular value.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

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.

Definition at line 108 of file dlas2.f.

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