DLARTG generate a plane rotation so that


    [  CS  SN  ]  .  [ F ]  =  [ R ]   where CS**2 + SN**2 = 1.


    [ -SN  CS  ]     [ G ]     [ 0 ]


 This is a slower, more accurate version of the BLAS1 routine DROTG,


 with the following other differences:


    F and G are unchanged on return.


    If G=0, then CS=1 and SN=0.


    If F=0 and (G .ne. 0), then CS=0 and SN=1 without doing any


       floating point operations (saves work in DBDSQR when


       there are zeros on the diagonal).


 If F exceeds G in magnitude, CS will be positive.

F

          F is DOUBLE PRECISION


          The first component of vector to be rotated.

G

          G is DOUBLE PRECISION


          The second component of vector to be rotated.

CS

          CS is DOUBLE PRECISION


          The cosine of the rotation.

SN

          SN is DOUBLE PRECISION


          The sine of the rotation.

R

          R is DOUBLE PRECISION


          The nonzero component of the rotated vector.


  This version has a few statements commented out for thread safety


  (machine parameters are computed on each entry). 10 feb 03, SJH.

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December 2016