double_gaussian_plot

  DOUBLE_GAUSSIAN_PLOT - calculate a double gaussian

  Computes responses to a double gaussian curve

  Z = DOUBLE_GAUSSIAN_PLOT(P, XI, WRAP), where

  P = parameters = [offset Rp Op Sigm Rn angle_offset]
  XI are the angles to be evaluated
  and WRAP is the wrap to be performed by ANGDIFFWRAP (usually 360)

  The curve is
    Z = offset + Rp*exp(-(angdiffwrap(xi-Op,wrap).^2)/(2*Sigm*Sigm))+...
         Rn*exp(-(angdiffwrap(xi-(Op+angle_offset),wrap)/(2*Sigm*Sigm)))