
DLASV2(l) ) DLASV2(l)
NAME
DLASV2  compute the singular value decomposition of a 2by2 triangular matrix [ F G ] [
0 H ]
SYNOPSIS
SUBROUTINE DLASV2( F, G, H, SSMIN, SSMAX, SNR, CSR, SNL, CSL )
DOUBLE PRECISION CSL, CSR, F, G, H, SNL, SNR, SSMAX, SSMIN
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 singu
lar 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 ].
ARGUMENTS
F (input) DOUBLE PRECISION
The (1,1) element of the 2by2 matrix.
G (input) DOUBLE PRECISION
The (1,2) element of the 2by2 matrix.
H (input) DOUBLE PRECISION
The (2,2) element of the 2by2 matrix.
SSMIN (output) DOUBLE PRECISION
abs(SSMIN) is the smaller singular value.
SSMAX (output) DOUBLE PRECISION
abs(SSMAX) is the larger singular value.
SNL (output) DOUBLE PRECISION
CSL (output) DOUBLE PRECISION The vector (CSL, SNL) is a unit left singular
vector for the singular value abs(SSMAX).
SNR (output) DOUBLE PRECISION
CSR (output) DOUBLE PRECISION The vector (CSR, SNR) is a unit right singular
vector for the singular value abs(SSMAX).
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.
LAPACK version 3.0 15 June 2000 DLASV2(l) 
