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slas2.f(3) LAPACK slas2.f(3)

NAME

slas2.f -

SYNOPSIS

Functions/Subroutines


subroutine slas2 (F, G, H, SSMIN, SSMAX)
SLAS2 computes singular values of a 2-by-2 triangular matrix.

Function/Subroutine Documentation

subroutine slas2 (realF, realG, realH, realSSMIN, realSSMAX)

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

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:

F


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

G


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

H


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

SSMIN


SSMIN is REAL
The smaller singular value.

SSMAX


SSMAX is REAL
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 slas2.f.

Author

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Tue Sep 25 2012 Version 3.4.2