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dlartgs.f(3) LAPACK dlartgs.f(3)

NAME

dlartgs.f -

SYNOPSIS

Functions/Subroutines


subroutine dlartgs (X, Y, SIGMA, CS, SN)
 
DLARTGS

Function/Subroutine Documentation

subroutine dlartgs (double precisionX, double precisionY, double precisionSIGMA, double precisionCS, double precisionSN)

DLARTGS
Purpose:
 
 DLARTGS generates a plane rotation designed to introduce a bulge in
 Golub-Reinsch-style implicit QR iteration for the bidiagonal SVD
 problem. X and Y are the top-row entries, and SIGMA is the shift.
 The computed CS and SN define a plane rotation satisfying


    [  CS  SN  ]  .  [ X^2 - SIGMA ]  =  [ R ],
    [ -SN  CS  ]     [    X * Y    ]     [ 0 ]


 with R nonnegative.  If X^2 - SIGMA and X * Y are 0, then the
 rotation is by PI/2.
 
Parameters:
X 
          X is DOUBLE PRECISION
          The (1,1) entry of an upper bidiagonal matrix.
 
Y 
          Y is DOUBLE PRECISION
          The (1,2) entry of an upper bidiagonal matrix.
 
SIGMA 
          SIGMA is DOUBLE PRECISION
          The shift.
 
CS 
          CS is DOUBLE PRECISION
          The cosine of the rotation.
 
SN 
          SN is DOUBLE PRECISION
          The sine of the rotation.
 
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
 
Definition at line 91 of file dlartgs.f.

Author

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