# -*- coding: utf-8 -*-
#
# balancedneuron.py
#
# This file is part of NEST.
#
# Copyright (C) 2004 The NEST Initiative
#
# NEST is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# NEST is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with NEST.  If not, see <http://www.gnu.org/licenses/>.

'''
Balanced neuron example
-----------------------

This script simulates a neuron driven by an excitatory and an
inhibitory population of neurons firing Poisson spike trains. The aim
is to find a firing rate for the inhibitory population that will make
the neuron fire at the same rate as the excitatory population.

Optimization is performed using the ``bisection`` method from Scipy,
simulating the network repeatedly.

This example is also shown in the article Eppler et al. (2009)
**PyNEST: A convenient interface to the NEST simulator**,
*Front. Neuroinform.* http://dx.doi.org/10.3389/neuro.11.012.2008
'''

'''
First, we import all necessary modules for simulation, analysis and
plotting. Scipy should be imported before nest.
'''

from scipy.optimize import bisect

import nest
import nest.voltage_trace

'''
Additionally, we set the verbosity using `set_verbosity` to
suppress info messages.
'''

nest.set_verbosity("M_WARNING")
nest.ResetKernel()

'''
Second, the simulation parameters are assigned to variables.
'''

t_sim = 25000.0  # how long we simulate
n_ex = 16000     # size of the excitatory population
n_in = 4000      # size of the inhibitory population
r_ex = 5.0       # mean rate of the excitatory population
r_in = 20.5      # initial rate of the inhibitory population
epsc = 45.0      # peak amplitude of excitatory synaptic currents
ipsc = -45.0     # peak amplitude of inhibitory synaptic currents
d = 1.0          # synaptic delay
lower = 15.0     # lower bound of the search interval
upper = 25.0     # upper bound of the search interval
prec = 0.01      # how close need the excitatory rates be

'''
Third, the nodes are created using `Create`. We store the returned
handles in variables for later reference.
'''

neuron = nest.Create("iaf_psc_alpha")
noise = nest.Create("poisson_generator", 2)
voltmeter = nest.Create("voltmeter")
spikedetector = nest.Create("spike_detector")

'''
Fourth, the excitatory `poisson_generator` (``noise[0]``) and the
`voltmeter` are configured using `SetStatus`, which expects a list of
node handles and a list of parameter dictionaries. The rate of the
inhibitory Poisson generator is set later. Note that we need not set
parameters for the neuron and the spike detector, since they have
satisfactory defaults.
'''

nest.SetStatus(noise, [{"rate": n_ex * r_ex}, {"rate": n_in * r_in}])
nest.SetStatus(voltmeter, {"withgid": True, "withtime": True})

'''
Fifth, the `iaf_psc_alpha` is connected to the `spike_detector` and the
`voltmeter`, as are the two Poisson generators to the neuron. The
command `Connect` has different variants. Plain `Connect` just takes
the handles of pre- and post-synaptic nodes and uses the default
values for weight and delay. It can also be called with a list of
weights, as in the connection of the noise below.
Note that the connection direction for the `voltmeter` is
reversed compared to the `spike_detector`, because it observes the
neuron instead of receiving events from it. Thus, `Connect` reflects
the direction of signal flow in the simulation kernel rather than the
physical process of inserting an electrode into the neuron. The latter
semantics is presently not available in NEST.
'''

nest.Connect(neuron, spikedetector)
nest.Connect(voltmeter, neuron)
nest.Connect(noise, neuron, syn_spec={'weight': [[epsc, ipsc]], 'delay': 1.0})

'''
To determine the optimal rate of the neurons in the inhibitory
population, the network is simulated several times for different
values of the inhibitory rate while measuring the rate of the target
neuron. This is done by calling `Simulate` until the rate of the
target neuron matches the rate of the neurons in the excitatory
population with a certain accuracy. The algorithm is implemented in
two steps:

First, the function ``output_rate`` is defined to measure the firing
rate of the target neuron for a given rate of the inhibitory neurons.
'''


def output_rate(guess):
    print("Inhibitory rate estimate: %5.2f Hz" % guess)
    rate = float(abs(n_in * guess))
    nest.SetStatus([noise[1]], "rate", rate)
    nest.SetStatus(spikedetector, "n_events", 0)
    nest.Simulate(t_sim)
    out = nest.GetStatus(spikedetector, "n_events")[0] * 1000.0 / t_sim
    print("  -> Neuron rate: %6.2f Hz (goal: %4.2f Hz)" % (out, r_ex))
    return out

'''
The function takes the firing rate of the inhibitory neurons as an
argument. It scales the rate with the size of the inhibitory
population and configures the inhibitory Poisson generator
(``noise[1]``) accordingly. Then, the spike counter of the
`spike_detector` is reset to zero. The network is simulated using
`Simulate`, which takes the desired simulation time in milliseconds
and advances the network state by this amount of time. During
simulation, the `spike_detector` counts the spikes of the target
neuron and the total number is read out at the end of the simulation
period. The return value of ``output_rate()`` is the firing rate of
the target neuron in Hz.

Second, the scipy function ``bisect`` is used to determine the optimal
firing rate of the neurons of the inhibitory population.
'''

in_rate = bisect(lambda x: output_rate(x) - r_ex, lower, upper, xtol=prec)
print("Optimal rate for the inhibitory population: %.2f Hz" % in_rate)

'''
The function ``bisect`` takes four arguments: first a function whose
zero crossing is to be determined. Here, the firing rate of the target
neuron should equal the firing rate of the neurons of the excitatory
population. Thus we define an anonymous function (using ``lambda``)
that returns the difference between the actual rate of the target
neuron and the rate of the excitatory Poisson generator, given a rate
for the inhibitory neurons. The next two arguments are the lower and
upper bound of the interval in which to search for the zero
crossing. The fourth argument of ``bisect`` is the desired relative
precision of the zero crossing.

Finally, we plot the target neuron's membrane potential as a function
of time.
'''

nest.voltage_trace.from_device(voltmeter)
