dlas2-f(3)

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

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

 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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