def get_two_taxon_neg_ll(
model,
em_probs, em_distns,
subs_counts,
ts, tv, syn, nonsyn, compo, asym_compo,
natural_theta,
):
"""
Get the negative log likelihood.
This function does not use the logarithms.
It is mostly for computing the hessian;
otherwise the version with the logarithms would probably be better.
The first param group is the model implementation.
The second param group is expectation-maximization stuff.
The third param group is the data.
The next param group consists of design matrices related to genetic code.
The next param group consist of free parameters of the model.
"""
# unpack some parameters
branch_length = natural_theta[0]
natural_model_theta = natural_theta[1:]
# compute the appropriately scaled transition matrices
pre_Qs = model.get_pre_Qs(
em_probs, em_distns,
ts, tv, syn, nonsyn, compo, asym_compo,
natural_model_theta)
eq_distns = model.get_distns(
em_probs, em_distns,
ts, tv, syn, nonsyn, compo, asym_compo,
natural_model_theta)
Ps = markovutil.get_branch_mix(em_probs, pre_Qs, eq_distns, branch_length)
# compute the mixture transition matrix
P_mix = algopy.zeros_like(Ps[0])
P_mix += em_probs[0] * (Ps[0].T * eq_distns[0]).T
P_mix += em_probs[1] * (Ps[1].T * eq_distns[1]).T
# compute the neg log likelihood
neg_ll = -algopy.sum(algopy.log(P_mix) * subs_counts)
print neg_ll
return neg_ll
def main(args):
# read the description of the genetic code
with open(args.code) as fin_gcode:
arr = list(csv.reader(fin_gcode, delimiter='\t'))
indices, aminos, codons = zip(*arr)
if [int(x) for x in indices] != range(len(indices)):
raise ValueError
aminos = [x.lower() for x in aminos]
nstop = aminos.count('stop')
if nstop not in (2, 3, 4):
raise Exception('expected 2 or 3 or 4 stop codons')
if any(x == 'stop' for x in aminos[:-nstop]):
raise Exception('expected stop codons at the end of the genetic code')
# trim the stop codons
aminos = aminos[:-nstop]
codons = codons[:-nstop]
# precompute some numpy ndarrays using the genetic code
ts = design.get_nt_transitions(codons)
tv = design.get_nt_transversions(codons)
syn = design.get_syn(codons, aminos)
nonsyn = design.get_nonsyn(codons, aminos)
compo = design.get_compo(codons)
nt_sinks = design.get_nt_sinks(codons)
asym_compo = np.transpose(nt_sinks, (1, 2, 0))
# read the (nstates, nstates) array of observed codon substitutions
subs_counts = np.loadtxt(args.count_matrix, dtype=float)
# trim the stop codons
subs_counts = subs_counts[:-nstop, :-nstop]
# compute some summaries of the observed codon substitutions
counts = np.sum(subs_counts, axis=0) + np.sum(subs_counts, axis=1)
log_counts = np.log(counts)
empirical_codon_distn = counts / float(np.sum(counts))
# make crude guesses about parameter values
blen = markovutil.guess_branch_length(subs_counts)
theta = args.model.get_natural_guess()
# Get the initial guesses for the EM parameters.
prior_probs = np.array([0.5, 0.5], dtype=float)
prior_em_distns = np.vstack((
empirical_codon_distn,
empirical_codon_distn,
))
# iteratively compute parameter estimates
for em_iteration_index in range(10):
# given parameter guesses, compute the pre-rate matrices
pre_Qs = args.model.get_pre_Qs(
prior_probs, prior_em_distns,
ts, tv, syn, nonsyn, compo, asym_compo,
theta)
# compute the appropriately scaled transition matrices
eq_distns = args.model.get_distns(
prior_probs, prior_em_distns,
ts, tv, syn, nonsyn, compo, asym_compo,
theta)
Ps = markovutil.get_branch_mix(
prior_probs, pre_Qs, eq_distns, blen)
# given parameter guesses, compute posterior expectations
post_probs, post_em_distns = get_posterior_expectations(
subs_counts, Ps, prior_probs, eq_distns)
# given posterior expectations, optimize the parameter guesses
encoded_theta = np.empty(len(theta) + 1, dtype=float)
encoded_theta[0] = np.log(blen)
encoded_theta[1:] = args.model.natural_to_encoded(theta)
# construct the neg log likelihood non-free params
neg_ll_args = (
args.model,
post_probs, post_em_distns,
subs_counts,
ts, tv, syn, nonsyn, compo, asym_compo,
)
# define the objective function and the gradient and hessian
f_encoded_theta = functools.partial(
get_two_taxon_neg_ll_encoded_theta, *neg_ll_args)
g_encoded_theta = functools.partial(eval_grad, f_encoded_theta)
h_encoded_theta = functools.partial(eval_hess, f_encoded_theta)
# do the search, using information about the gradient and hessian
results = scipy.optimize.minimize(
f_encoded_theta,
encoded_theta,
method=args.minimization_method,
jac=g_encoded_theta,
hess=h_encoded_theta,
)
# extract and decode the maximum likelihood estimates
encoded_xopt = results.x
mle_log_blen = encoded_xopt[0]
mle_blen = np.exp(mle_log_blen)
model_encoded_xopt = encoded_xopt[1:]
model_xopt = args.model.encoded_to_natural(
model_encoded_xopt)
xopt = np.empty_like(encoded_xopt)
xopt[0] = mle_blen
xopt[1:] = model_xopt
# report a summary of the maximum likelihood search
print 'raw results from the minimization:'
print results
print
print 'max likelihood branch length (expected number of substitutions):'
print mle_blen
print
print 'max likelihood estimates of other model parameters:'
print model_xopt
print
print 'posterior mixture probabilities:'
print post_probs
print
# get ready for the next iteration if we continue
blen = mle_blen
#theta = model_xopt
prior_probs = post_probs
prior_em_distns = post_em_distns
