Truncate phase function in MYSTIC: The phasefunctions are set to zero for mu>mucut. The extinction coefficient etc. are scaled accordingly. Optional settings are mc_delta_scaling mucut and mc_delta_scaling mucut n_start, where mucut is 0.99 by default. The value n_start defines after which scattering order delta-scaling is applied, before that scattering order, the real phase function is applied. Default is 0, i.e. the delta-scaled phase function is applied from the beginning.