LARTG - 5.2 English - 68552

   LARTG 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 SROTG,
   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 SBDSQR when
         there are zeros on the diagonal).

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