def find_foh_coeff(count_begin, count_final, o_array):

    """
    Finds the foh coefficient for the linear fly trap model.  The foh coefficient specifies 
    the fraction of flies which transition from "on the trap" to "in the trap, but hidden" 
    during a given time step.


    Arguments:

      count_begin  =  number of flies in trap at the start of the trial 
      count_final  =  number of flies in trap at the end of the trial 
      o_array      =  array of "on trap" counts giving number of flies on the trap at 
                      each time step 
    Returns:

      foh          =  coefficient specifying the fraction of flies transistioning from 
                      "on trap" o[n] to "in trap hidden" h[n] during a given time step 

    """

    foh = (count_final - count_begin)/float(o_array.sum())
    return foh