approx_theta_post_s2 function

Find optimal theta of a CNV segment using forward-backward; uses a 2-state allele HMM

approx_theta_post_s2(
  pAD,
  DP,
  R,
  p_s,
  upper = 0.499,
  start = 0.25,
  gamma = 20,
  r = 0.015
)