dlas2.f (3)  Linux Manuals
NAME
dlas2.f 
SYNOPSIS
Functions/Subroutines
subroutine dlas2 (F, G, H, SSMIN, SSMAX)
DLAS2 computes singular values of a 2by2 triangular matrix.
Function/Subroutine Documentation
subroutine dlas2 (double precisionF, double precisionG, double precisionH, double precisionSSMIN, double precisionSSMAX)
DLAS2 computes singular values of a 2by2 triangular matrix.
Purpose:

DLAS2 computes the singular values of the 2by2 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 2by2 matrix.
GG is DOUBLE PRECISION The (1,2) element of the 2by2 matrix.
HH is DOUBLE PRECISION The (2,2) element of the 2by2 matrix.
SSMINSSMIN is DOUBLE PRECISION The smaller singular value.
SSMAXSSMAX 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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