def ais_latent_network_given_A(x0, graph_model, graph_sampler, N_samples=1000, B=100,
steps_per_B=11):
"""
Use AIS to approximate the marginal likelihood of a latent network model
"""
import pdb; pdb.set_trace()
betas = np.linspace(0,1,B)
# Sample m points
log_weights = np.zeros(N_samples)
for m in range(N_samples):
# Sample a new set of graph parameters from the prior
x = copy.deepcopy(x0)
# print "M: %d" % m
# Sample mus from each of the intermediate distributions,
# starting with a draw from the prior.
samples = []
# Ratios correspond to the 'f_{n-1}(x_{n-1})/f_{n}(x_{n-1})' values in Neal's paper
ratios = np.zeros(B-1)
# Sample the intermediate distributions
for (n,beta) in zip(range(1,B), betas[1:]):
# print "M: %d\tBeta: %.3f" % (m,beta)
sys.stdout.write("M: %d\tBeta: %.3f \r" % (m,beta))
sys.stdout.flush()
# Set the likelihood scale (beta) in the graph model
graph_model.lkhd_scale.set_value(beta)
# Take 100 steps per beta
for s in range(steps_per_B):
x = graph_sampler.update(x)
# Compute the ratio of this sample under this distribution and the previous distribution
curr_lkhd = seval(graph_model.log_p,
graph_model.get_variables(),
x['net']['graph'])
graph_model.lkhd_scale.set_value(betas[n-1])
prev_lkhd = seval(graph_model.log_p,
graph_model.get_variables(),
x['net']['graph'])
ratios[n-1] = curr_lkhd - prev_lkhd
# Compute the log weight of this sample
log_weights[m] = np.sum(ratios)
print ""
print "W: %f" % log_weights[m]
# Compute the mean of the weights to get an estimate of the normalization constant
log_Z = -np.log(N_samples) + logsumexp(log_weights)
return log_Z
def plot(self,
xs,
ax=None,
title=None,
vmin=None,
vmax=None,
cmap=rwb_cmap):
# Ensure sample is a list
if not isinstance(xs, list):
xs = [xs]
# Get the weight matrix and adjacency matrix
wvars = self.population.network.weights.get_variables()
Ws = np.array([
seval(self.population.network.weights.W, wvars,
x['net']['weights']) for x in xs
])
gvars = self.population.network.graph.get_variables()
As = np.array([
seval(self.population.network.graph.A, gvars, x['net']['graph'])
for x in xs
])
# Compute the effective connectivity matrix
W_inf = np.mean(Ws * As, axis=0)
# Make sure bounds are set
if None in (vmax, vmin):
vmax = np.amax(np.abs(W_inf))
vmin = -vmax
# Create a figure if necessary
if ax is None:
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
px_per_node = 10
im = ax.imshow(np.kron(W_inf, np.ones((px_per_node, px_per_node))),
vmin=vmin,
vmax=vmax,
extent=[0, 1, 0, 1],
interpolation='nearest',
cmap=cmap)
ax.set_title(title)
def compute_log_prior(self, vars):
""" Compute the log joint probability under a given set of variables
"""
lp = 0.0
# Get set of symbolic variables
syms = self.get_variables()
lp += seval(self.latent.log_p, syms['latent'], vars['latent'])
lp += seval(self.network.log_p, syms['net'], vars['net'])
for n in range(self.N):
nvars = self.extract_vars(vars, n)
lp += seval(self.glm.log_prior, syms, nvars)
return lp
def _eval_state_helper(self, syms, d, vars):
""" Helper function to recursively evaluate state variables
"""
state = {}
for (k,v) in d.items():
if isinstance(v,dict):
state[k] = self._eval_state_helper(syms, v, vars)
else:
state[k] = seval(v, syms, vars)
return state
def _eval_state_helper(self, syms, d, vars):
""" Helper function to recursively evaluate state variables
"""
state = {}
for (k, v) in d.items():
if isinstance(v, dict):
state[k] = self._eval_state_helper(syms, v, vars)
else:
state[k] = seval(v, syms, vars)
return state
def grad_nlp(x_glm_vec, x):
"""
Helper function to compute the gradient of negative log posterior for
a given set of GLM parameters. The parameters are passed in as a vector.
"""
x_glm = unpackdict(x_glm_vec, glm_shapes)
set_vars(glm_syms, x['glm'], x_glm)
glp = seval(g_glm_logprior,
syms,
x)
# Add the likelihood of each data sequence
for data in population.data_sequences:
# Set the data
population.set_data(data)
glp += seval(g_glm_ll,
syms,
x)
return -1.0 * glp
def plot(self, xs, ax=None, name='location_provider', color='k'):
"""
Plot a histogram of the inferred locations for each neuron
"""
# Ensure sample is a list
if not isinstance(xs, list):
xs = [xs]
if name not in xs[0]['latent']:
return
# Get the locations
loccomp = self.population.latent.latentdict[name]
locprior = loccomp.location_prior
locvars = loccomp.get_variables()
Ls = np.array([seval(loccomp.Lmatrix,
locvars, x['latent'][name])
for x in xs])
[N_smpls, N, D] = Ls.shape
for n in range(N):
# plt.subplot(1,N,n+1, aspect=1.0)
# plt.title('N: %d' % n)
if N_smpls == 1:
if D == 1:
plt.plot([Ls[0,n,0], Ls[0,n,0]],
[0,2], color=color, lw=2)
elif D == 2:
ax.plot(Ls[0,n,1], Ls[0,n,0], 's',
color=color, markerfacecolor=color)
ax.text(Ls[0,n,1]+0.25, Ls[0,n,0]+0.25, '%d' % n,
color=color)
# Set the limits
ax.set_xlim((locprior.min0-0.5, locprior.max0+0.5))
ax.set_ylim((locprior.max1+0.5, locprior.min1-0.5))
else:
raise Exception("Only plotting locs of dim <= 2")
else:
# Plot a histogram of samples
if D == 1:
ax.hist(Ls[:,n,0], bins=20, normed=True, color=color)
elif D == 2:
ax.hist2d(Ls[:,n,1], Ls[:,n,0], bins=np.arange(-0.5,5), cmap='Reds', alpha=0.5, normed=True)
# Set the limits
ax.set_xlim((locprior.min0-0.5, locprior.max0+0.5))
ax.set_ylim((locprior.max1+0.5, locprior.min1-0.5))
# ax.colorbar()
else:
raise Exception("Only plotting locs of dim <= 2")
def grad_nlp(x_glm_vec, x):
"""
Helper function to compute the gradient of negative log posterior for
a given set of GLM parameters. The parameters are passed in as a vector.
"""
x_network = unpackdict(x_glm_vec, network_shapes)
set_vars(network_syms, x['net'], x_network)
glp = seval(g_network_logprior,
syms,
x)
return -1.0 * glp
def plot(self, xs, ax=None, title=None, vmin=None, vmax=None, cmap=rwb_cmap):
# Ensure sample is a list
if not isinstance(xs, list):
xs = [xs]
# Get the weight matrix and adjacency matrix
wvars = self.population.network.weights.get_variables()
Ws = np.array([seval(self.population.network.weights.W,
wvars, x['net']['weights'])
for x in xs])
gvars = self.population.network.graph.get_variables()
As = np.array([seval(self.population.network.graph.A,
gvars, x['net']['graph'])
for x in xs])
# Compute the effective connectivity matrix
W_inf = np.mean(Ws*As, axis=0)
# Make sure bounds are set
if None in (vmax,vmin):
vmax = np.amax(np.abs(W_inf))
vmin = -vmax
# Create a figure if necessary
if ax is None:
fig = plt.figure()
ax = fig.add_subplot(1,1,1)
px_per_node = 10
im = ax.imshow(np.kron(W_inf,np.ones((px_per_node,px_per_node))),
vmin=vmin, vmax=vmax,
extent=[0,1,0,1],
interpolation='nearest',
cmap=cmap)
ax.set_title(title)
def compute_log_prior(self, vars):
""" Compute the log joint probability under a given set of variables
"""
lp = 0.0
# Get set of symbolic variables
syms = self.get_variables()
lp += seval(self.latent.log_p,
syms['latent'],
vars['latent'])
lp += seval(self.network.log_p,
syms['net'],
vars['net'])
for n in range(self.N):
nvars = self.extract_vars(vars, n)
lp += seval(self.glm.log_prior,
syms,
nvars)
return lp
def compute_ll(self, vars):
""" Compute the log likelihood under a given set of variables
"""
ll = 0.0
# Get set of symbolic variables
syms = self.get_variables()
# Add the likelihood from each GLM
for n in range(self.N):
nvars = self.extract_vars(vars, n)
ll += seval(self.glm.ll, syms, nvars)
return ll
def compute_ll(self, vars):
""" Compute the log likelihood under a given set of variables
"""
ll = 0.0
# Get set of symbolic variables
syms = self.get_variables()
# Add the likelihood from each GLM
for n in range(self.N):
nvars = self.extract_vars(vars, n)
ll += seval(self.glm.ll,
syms,
nvars)
return ll
class Population:
"""
Population connected GLMs.
"""
def __init__(self, model):
"""
Initialize the population of GLMs connected by a network.
"""
self.model = model
self.N = model['N']
# Initialize a list of data sequences
self.data_sequences = []
# Initialize latent variables of the population
self.latent = LatentVariables(model)
# Create a network model to connect the GLMs
self.network = Network(model, self.latent)
# Create a single GLM that is shared across neurons
# This is to simplify the model and reuse parameters.
# Basically it speeds up the gradient calculations since we
# can manually leverage conditional independencies among GLMs
self.glm = Glm(model, self.network, self.latent)
def compute_log_p(self, vars):
""" Compute the log joint probability under a given set of variables
"""
lp = 0.0
lp += self.compute_log_prior(vars)
# Add the likelihood of each data sequence
for data in self.data_sequences:
self.set_data(data)
lp += self.compute_ll(vars)
return lp
def compute_log_prior(self, vars):
""" Compute the log joint probability under a given set of variables
"""
lp = 0.0
# Get set of symbolic variables
syms = self.get_variables()
lp += seval(self.latent.log_p, syms['latent'], vars['latent'])
lp += seval(self.network.log_p, syms['net'], vars['net'])
for n in range(self.N):
nvars = self.extract_vars(vars, n)
lp += seval(self.glm.log_prior, syms, nvars)
return lp
def compute_ll(self, vars):
""" Compute the log likelihood under a given set of variables
"""
ll = 0.0
# Get set of symbolic variables
syms = self.get_variables()
# Add the likelihood from each GLM
for n in range(self.N):
nvars = self.extract_vars(vars, n)
ll += seval(self.glm.ll, syms, nvars)
return ll
def eval_state(self, vars):
""" Evaluate the population state expressions given the parameters,
e.g. the stimulus response curves from the basis function weights.
"""
# Get set of symbolic variables
syms = self.get_variables()
# Get the symbolic state expression to evaluate
state_vars = self.get_state()
state = {}
state['latent'] = self._eval_state_helper(syms['latent'],
state_vars['latent'],
vars['latent'])
state['net'] = self._eval_state_helper(syms['net'], state_vars['net'],
vars['net'])
glm_states = []
for n in np.arange(self.N):
nvars = self.extract_vars(vars, n)
glm_states.append(
self._eval_state_helper(syms, state_vars['glm'], nvars))
state['glms'] = glm_states
# Finally, evaluate the log probability and the log likelihood
# state['logp'] = self.compute_log_p(vars)
state['logprior'] = self.compute_log_prior(vars)
state['ll'] = self.compute_ll(vars)
state['logp'] = state['ll'] + state['logprior']
return state
def _eval_state_helper(self, syms, d, vars):
""" Helper function to recursively evaluate state variables
"""
state = {}
for (k, v) in d.items():
if isinstance(v, dict):
state[k] = self._eval_state_helper(syms, v, vars)
else:
state[k] = seval(v, syms, vars)
return state
def get_variables(self):
""" Get a list of all variables
"""
v = {}
v['latent'] = self.latent.get_variables()
v['net'] = self.network.get_variables()
v['glm'] = self.glm.get_variables()
return v
def set_hyperparameters(self, model):
""" Set the hyperparameters of the model
"""
self.latent.set_hyperparameters(model)
self.network.set_hyperparameters(model)
self.glm.set_hyperparameters(model)
def sample(self):
"""
Sample parameters of the GLM from the prior
"""
v = {}
v['latent'] = self.latent.sample(v)
v['net'] = self.network.sample(v)
v['glms'] = []
for n in range(self.N):
xn = self.glm.sample(v)
xn['n'] = n
v['glms'].append(xn)
return v
def extract_vars(self, vals, n):
""" Hacky helper function to extract the variables for only the
n-th GLM.s
"""
newvals = {}
for (k, v) in vals.items():
if k == 'glms':
newvals['glm'] = v[n]
else:
newvals[k] = v
return newvals
def get_state(self):
""" Get the 'state' of the system in symbolic Theano variables
"""
state = {}
state['latent'] = self.latent.get_state()
state['net'] = self.network.get_state()
state['glm'] = self.glm.get_state()
return state
def preprocess_data(self, data):
"""
Preprocess the data to compute filtered stimuli, spike trains, etc.
"""
assert isinstance(data, dict), 'Data must be a dictionary'
self.latent.preprocess_data(data)
self.network.preprocess_data(data)
self.glm.preprocess_data(data)
data['preprocessed'] = True
return data
def add_data(self, data, set_as_current_data=True):
"""
Add another data sequence to the population. Recursively call components
to prepare the new data sequence. E.g. the background model may preprocess
the stimulus with a set of basis filters.
"""
# TODO: Figure out how to handle time varying weights with multiple
# data sequences. Maybe we only allow one sequence.
assert isinstance(data, dict), 'Data must be a dictionary'
# Check for spike times in the data array
assert 'S' in data, 'Data must contain an array of spike times'
assert isinstance(data['S'],
np.ndarray), 'Spike times must be a numpy array'
if 'preprocessed' not in data or not data['preprocessed']:
data = self.preprocess_data(data)
# Add the data to the list
self.data_sequences.append(data)
# By default, we set this as the current dataset
if set_as_current_data:
self.set_data(data)
def set_data(self, data):
"""
Condition on the data
"""
assert 'preprocessed' in data and data['preprocessed'] == True, \
'Data must be preprocessed before it can be set'
self.latent.set_data(data)
self.network.set_data(data)
self.glm.set_data(data)
def simulate(self, vars, (T_start, T_stop), dt, stim, dt_stim):
""" Simulate spikes from a network of coupled GLMs
:param vars - the variables corresponding to each GLM
:type vars list of N variable vectors
:param dt - time steps to simulate
:rtype TxN matrix of spike counts in each bin
"""
# Initialize the background rates
N = self.model['N']
t = np.arange(T_start, T_stop, dt)
t_ind = np.arange(int(T_start / dt), int(T_stop / dt))
assert len(t) == len(t_ind)
nT = len(t)
# Get set of symbolic variables
syms = self.get_variables()
# Initialize the background rate
X = np.zeros((nT, N))
for n in np.arange(N):
nvars = self.extract_vars(vars, n)
X[:, n] = seval(self.glm.bias_model.I_bias, syms, nvars)
# Add stimulus induced currents if given
temp_data = {'S': np.zeros((nT, N)), 'stim': stim, 'dt_stim': dt_stim}
self.add_data(temp_data)
for n in np.arange(N):
nvars = self.extract_vars(vars, n)
X[:, n] += seval(self.glm.bkgd_model.I_stim, syms, nvars)
print "Max background rate: %s" % str(
self.glm.nlin_model.f_nlin(np.amax(X)))
# Remove the temp data from the population data sequences
self.data_sequences.pop()
# Get the impulse response functions
imps = []
for n_post in np.arange(N):
nvars = self.extract_vars(vars, n_post)
imps.append(seval(self.glm.imp_model.impulse, syms, nvars))
imps = np.transpose(np.array(imps), axes=[1, 0, 2])
T_imp = imps.shape[2]
# Debug: compute effective weights
# tt_imp = dt*np.arange(T_imp)
# Weff = np.trapz(imps, tt_imp, axis=2)
# print "Effective impulse weights: "
# print Weff
# Iterate over each time step and generate spikes
S = np.zeros((nT, N))
acc = np.zeros(N)
thr = -np.log(np.random.rand(N))
# TODO: Handle time-varying weights appropriately
time_varying_weights = False
if not time_varying_weights:
At = np.tile(
np.reshape(
seval(self.network.graph.A, syms['net'], vars['net']),
[N, N, 1]), [1, 1, T_imp])
Wt = np.tile(
np.reshape(
seval(self.network.weights.W, syms['net'], vars['net']),
[N, N, 1]), [1, 1, T_imp])
# Count the number of exceptions arising from more spikes per bin than allowable
n_exceptions = 0
for t in np.arange(nT):
# Update accumulator
if np.mod(t, 10000) == 0:
print "Iteration %d" % t
# TODO Handle nonlinearities with variables
lam = self.glm.nlin_model.f_nlin(X[t, :])
acc = acc + lam * dt
# Spike if accumulator exceeds threshold
i_spk = acc > thr
S[t, i_spk] += 1
n_spk = np.sum(i_spk)
# Compute the length of the impulse response
t_imp = np.minimum(nT - t - 1, T_imp)
# Get the instantaneous connectivity
if time_varying_weights:
# TODO: Really get the time-varying weights
At = np.tile(
np.reshape(
seval(self.network.graph.A, syms['net'], vars['net']),
[N, N, 1]), [1, 1, t_imp])
Wt = np.tile(
np.reshape(
seval(self.network.weights.W, syms['net'],
vars['net']), [N, N, 1]), [1, 1, t_imp])
# Iterate until no more spikes
# Cap the number of spikes in a time bin
max_spks_per_bin = 10
while n_spk > 0:
if np.any(S[t, :] >= max_spks_per_bin):
n_exceptions += 1
break
# Add weighted impulse response to activation of other neurons)
X[t + 1:t + t_imp + 1, :] += np.sum(
At[i_spk, :, :t_imp] * Wt[i_spk, :, :t_imp] *
imps[i_spk, :, :t_imp], 0).T
# Subtract threshold from the accumulator
acc -= thr * i_spk
acc[acc < 0] = 0
# Set new threshold after spike
thr[i_spk] = -np.log(np.random.rand(n_spk))
i_spk = acc > thr
S[t, i_spk] += 1
n_spk = np.sum(i_spk)
#if np.any(S[t,:]>10):
# import pdb
# pdb.set_trace()
# raise Exception("More than 10 spikes in a bin! Decrease variance on impulse weights or decrease simulation bin width.")
# DEBUG:
tt = dt * np.arange(nT)
lam = np.zeros_like(X)
for n in np.arange(N):
lam[:, n] = self.glm.nlin_model.f_nlin(X[:, n])
print "Max firing rate (post sim): %f" % np.max(lam)
E_nS = np.trapz(lam, tt, axis=0)
nS = np.sum(S, 0)
print "Sampled %s spikes." % str(nS)
print "Expected %s spikes." % str(E_nS)
if np.any(np.abs(nS - E_nS) > 3 * np.sqrt(E_nS)):
print "ERROR: Actual num spikes (%s) differs from expected (%s) by >3 std." % (
str(nS), str(E_nS))
print "Number of exceptions arising from multiple spikes per bin: %d" % n_exceptions
return S, X
def plot(self, xs, ax=None, name='location_provider', color='k'):
"""
Plot a histogram of the inferred locations for each neuron
"""
# Ensure sample is a list
if not isinstance(xs, list):
xs = [xs]
if name not in xs[0]['latent']:
return
# Get the locations
loccomp = self.population.latent.latentdict[name]
locprior = loccomp.location_prior
locvars = loccomp.get_variables()
Ls = np.array(
[seval(loccomp.Lmatrix, locvars, x['latent'][name]) for x in xs])
[N_smpls, N, D] = Ls.shape
for n in range(N):
# plt.subplot(1,N,n+1, aspect=1.0)
# plt.title('N: %d' % n)
if N_smpls == 1:
if D == 1:
plt.plot([Ls[0, n, 0], Ls[0, n, 0]], [0, 2],
color=color,
lw=2)
elif D == 2:
ax.plot(Ls[0, n, 1],
Ls[0, n, 0],
's',
color=color,
markerfacecolor=color)
ax.text(Ls[0, n, 1] + 0.25,
Ls[0, n, 0] + 0.25,
'%d' % n,
color=color)
# Set the limits
ax.set_xlim((locprior.min0 - 0.5, locprior.max0 + 0.5))
ax.set_ylim((locprior.max1 + 0.5, locprior.min1 - 0.5))
else:
raise Exception("Only plotting locs of dim <= 2")
else:
# Plot a histogram of samples
if D == 1:
ax.hist(Ls[:, n, 0], bins=20, normed=True, color=color)
elif D == 2:
ax.hist2d(Ls[:, n, 1],
Ls[:, n, 0],
bins=np.arange(-0.5, 5),
cmap='Reds',
alpha=0.5,
normed=True)
# Set the limits
ax.set_xlim((locprior.min0 - 0.5, locprior.max0 + 0.5))
ax.set_ylim((locprior.max1 + 0.5, locprior.min1 - 0.5))
# ax.colorbar()
else:
raise Exception("Only plotting locs of dim <= 2")
