def get_likelihood(test_statistics, dhisto, dtypes, lib, params):
''' get likelihood object
:type test_statistics: a string
:param test_statistics: test statistics method
chi2 / modchi2 / barlow / poisson
:type dhisto: a dictionary
:param dhisto: data histogram {'H':H, 'H2':H2}
:type dtypes: a list / numpy array
:param dtypes: list of dtypes involved
:type lib: a Library object
:param lib: library object to get baseline events
:type params: a dictionary
:param params: minimizer start values by user
:return LH: a Likelihood class
LH: likelihood object
'''
LH = Likelihood(dhisto, test_statistics, verbose=verbose)
## special info for barlow LLH
if 'barlow' in test_statistics:
events = collect_events(lib, dtypes)
unhistos, norms = get_barlow_params(events, params)
LH.set_barlow(unhistos, norms)
return LH
