dlas2.f(3)

NAME
dlas2.f -

SYNOPSIS

  Functions/Subroutines

subroutine dlas2 (F, G, H, SSMIN, SSMAX)
DLAS2 computes singular values of a 2-by-2 triangular matrix.

Function/Subroutine Documentation

  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.

Author

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