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slasv2.f(3) LAPACK slasv2.f(3)

NAME

slasv2.f -

SYNOPSIS

Functions/Subroutines


subroutine slasv2 (F, G, H, SSMIN, SSMAX, SNR, CSR, SNL, CSL)
SLASV2 computes the singular value decomposition of a 2-by-2 triangular matrix.

Function/Subroutine Documentation

subroutine slasv2 (realF, realG, realH, realSSMIN, realSSMAX, realSNR, realCSR, realSNL, realCSL)

SLASV2 computes the singular value decomposition of a 2-by-2 triangular matrix.

Purpose:


SLASV2 computes the singular value decomposition of a 2-by-2
triangular matrix
[ F G ]
[ 0 H ].
On return, abs(SSMAX) is the larger singular value, abs(SSMIN) is the
smaller singular value, and (CSL,SNL) and (CSR,SNR) are the left and
right singular vectors for abs(SSMAX), giving the decomposition
[ CSL SNL ] [ F G ] [ CSR -SNR ] = [ SSMAX 0 ]
[-SNL CSL ] [ 0 H ] [ SNR CSR ] [ 0 SSMIN ].

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
abs(SSMIN) is the smaller singular value.

SSMAX


SSMAX is REAL
abs(SSMAX) is the larger singular value.

SNL


SNL is REAL

CSL


CSL is REAL
The vector (CSL, SNL) is a unit left singular vector for the
singular value abs(SSMAX).

SNR


SNR is REAL

CSR


CSR is REAL
The vector (CSR, SNR) is a unit right singular vector for the
singular value abs(SSMAX).

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Further Details:


Any input parameter may be aliased with any output parameter.
Barring over/underflow and assuming a guard digit in subtraction, all
output quantities are correct to within a few units in the last
place (ulps).
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 139 of file slasv2.f.

Author

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Tue Sep 25 2012 Version 3.4.2