LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
slartgs.f File Reference

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Functions/Subroutines

subroutine SLARTGS (X, Y, SIGMA, CS, SN)
 SLARTGS

Function/Subroutine Documentation

subroutine SLARTGS ( REAL  X,
REAL  Y,
REAL  SIGMA,
REAL  CS,
REAL  SN 
)

SLARTGS

Download SLARTGS + dependencies [TGZ] [ZIP] [TXT]
Purpose:

 SLARTGS 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:
[in]X
          X is REAL
          The (1,1) entry of an upper bidiagonal matrix.
 
[in]Y
          Y is REAL
          The (1,2) entry of an upper bidiagonal matrix.
 
[in]SIGMA
          SIGMA is REAL
          The shift.
 
[out]CS
          CS is REAL
          The cosine of the rotation.
 
[out]SN
          SN is REAL
          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 slartgs.f.

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