
dlasv2.f(3) LAPACK dlasv2.f(3)
NAME
dlasv2.f 
SYNOPSIS
Functions/Subroutines
subroutine dlasv2 (F, G, H, SSMIN, SSMAX, SNR, CSR, SNL, CSL)
DLASV2 computes the singular value decomposition of a 2by2 triangular matrix.
Function/Subroutine Documentation
subroutine dlasv2 (double precisionF, double precisionG, double precisionH, double
precisionSSMIN, double precisionSSMAX, double precisionSNR, double precisionCSR, double
precisionSNL, double precisionCSL)
DLASV2 computes the singular value decomposition of a 2by2 triangular matrix.
Purpose:
DLASV2 computes the singular value decomposition of a 2by2
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 DOUBLE PRECISION
The (1,1) element of the 2by2 matrix.
G
G is DOUBLE PRECISION
The (1,2) element of the 2by2 matrix.
H
H is DOUBLE PRECISION
The (2,2) element of the 2by2 matrix.
SSMIN
SSMIN is DOUBLE PRECISION
abs(SSMIN) is the smaller singular value.
SSMAX
SSMAX is DOUBLE PRECISION
abs(SSMAX) is the larger singular value.
SNL
SNL is DOUBLE PRECISION
CSL
CSL is DOUBLE PRECISION
The vector (CSL, SNL) is a unit left singular vector for the
singular value abs(SSMAX).
SNR
SNR is DOUBLE PRECISION
CSR
CSR is DOUBLE PRECISION
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 dlasv2.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dlasv2.f(3) 
