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slartgs.f(3) LAPACK slartgs.f(3)

NAME

slartgs.f

SYNOPSIS

Functions/Subroutines


subroutine slartgs (X, Y, SIGMA, CS, SN)
SLARTGS generates a plane rotation designed to introduce a bulge in implicit QR iteration for the bidiagonal SVD problem.

Function/Subroutine Documentation

subroutine slartgs (real X, real Y, real SIGMA, real CS, real SN)

SLARTGS generates a plane rotation designed to introduce a bulge in implicit QR iteration for the bidiagonal SVD problem.

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:

X 



          X is REAL


          The (1,1) entry of an upper bidiagonal matrix.

Y



          Y is REAL


          The (1,2) entry of an upper bidiagonal matrix.

SIGMA



          SIGMA is REAL


          The shift.

CS



          CS is REAL


          The cosine of the rotation.

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 2017

Definition at line 92 of file slartgs.f.

Author

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