* phi_polar.kumac - plot the polarization of the GlueX photon
*                   as a function of theta*E/m and phi of the
*                   bremsstrahlung emission.  The polarization
*                   is plotted at the primary peak of 9 GeV for
*                   and electron beam energy of 12 GeV.
macro make id=200 Emax=12 Epeak=9.0 emit=1e-8 dist=75 coldiam=3.4e-3 thetamax=0.5
  call cobrems.f77($rsigma([Emax]),$rsigma([Epeak]),$rsigma([emit]),$rsigma([dist]),$rsigma([coldiam]),1)
  id1=[id]+1
  id2=[id]+2
  id3=[id]+3
  id4=[id]+4
  xpeak=$rsigma([Epeak]/[Emax])
  thetamax=$rsigma([coldiam]/2/[dist]*[Emax]/0.511e-3)
  xmin=$rsigma([xpeak]/([xpeak]+(1-[xpeak])*([thetamax]**2+1)))
  fun2 [id1] rpara([xpeak]/([xpeak]+(1-[xpeak])*(x**2+1)),x**2,y) 50 0 [thetamax] 50 0 3.1416
  fun2 [id2] rortho([xpeak]/([xpeak]+(1-[xpeak])*(x**2+1)),x**2,y) 50 0 [thetamax] 50 0 3.1416
  add [id1] [id2] [id3] 1 1
  add [id1] [id2] [id4] 1 -1
  div [id4] [id3] [id]
  *op/add [id] [id] [id] $rsigma(6./7) 0
  opt utit
  h/pl [id] surf
  atit 'theta (m/E)' 'phi (rad)' 'peak polarization'
  opt htit
return