dlartgs.f(3)

NAME
dlartgs.f -

SYNOPSIS

  Functions/Subroutines

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

Function/Subroutine Documentation

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

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

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:
    September 2012

Definition at line 91 of file dlartgs.f.

Author

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