# brainpy.integrators.ode.ExponentialEuler#

class brainpy.integrators.ode.ExponentialEuler(f, var_type=None, dt=None, name=None, show_code=False, dyn_vars=None, state_delays=None, neutral_delays=None)[source]#

Exponential Euler method using automatic differentiation.

This method uses brainpy.math.vector_grad to automatically infer the linear part of the given function. Therefore, it has minimal constraints on your derivative function. Arbitrary complex functions can be numerically integrated with this method.

Examples

Here is an example uses `ExponentialEuler` to implement HH neuron model.

```>>> import brainpy as bp
>>> import brainpy.math as bm
>>>
>>> class HH(bp.dyn.NeuGroup):
>>>   def __init__(self, size, ENa=55., EK=-90., EL=-65, C=1.0, gNa=35., gK=9.,
>>>                gL=0.1, V_th=20., phi=5.0, name=None):
>>>     super(HH, self).__init__(size=size, name=name)
>>>
>>>     # parameters
>>>     self.ENa = ENa
>>>     self.EK = EK
>>>     self.EL = EL
>>>     self.C = C
>>>     self.gNa = gNa
>>>     self.gK = gK
>>>     self.gL = gL
>>>     self.V_th = V_th
>>>     self.phi = phi
>>>
>>>     # variables
>>>     self.V = bm.Variable(bm.ones(size) * -65.)
>>>     self.h = bm.Variable(bm.ones(size) * 0.6)
>>>     self.n = bm.Variable(bm.ones(size) * 0.32)
>>>     self.spike = bm.Variable(bm.zeros(size, dtype=bool))
>>>     self.input = bm.Variable(bm.zeros(size))
>>>
>>>     # functions
>>>     self.int_h = bp.ode.ExponentialEuler(self.dh)
>>>     self.int_n = bp.ode.ExponentialEuler(self.dn)
>>>     self.int_V = bp.ode.ExponentialEuler(self.dV)
>>>
>>>   def dh(self, h, t, V):
>>>     alpha = 0.07 * bm.exp(-(V + 58) / 20)
>>>     beta = 1 / (bm.exp(-0.1 * (V + 28)) + 1)
>>>     dhdt = self.phi * (alpha * (1 - h) - beta * h)
>>>     return dhdt
>>>
>>>   def dn(self, n, t, V):
>>>     alpha = -0.01 * (V + 34) / (bm.exp(-0.1 * (V + 34)) - 1)
>>>     beta = 0.125 * bm.exp(-(V + 44) / 80)
>>>     dndt = self.phi * (alpha * (1 - n) - beta * n)
>>>     return dndt
>>>
>>>   def dV(self, V, t, h, n, Iext):
>>>     m_alpha = -0.1 * (V + 35) / (bm.exp(-0.1 * (V + 35)) - 1)
>>>     m_beta = 4 * bm.exp(-(V + 60) / 18)
>>>     m = m_alpha / (m_alpha + m_beta)
>>>     INa = self.gNa * m ** 3 * h * (V - self.ENa)
>>>     IK = self.gK * n ** 4 * (V - self.EK)
>>>     IL = self.gL * (V - self.EL)
>>>     dVdt = (- INa - IK - IL + Iext) / self.C
>>>
>>>     return dVdt
>>>
>>>   def update(self, tdi):
>>>     h = self.int_h(self.h, tdi.t, self.V, dt=tdi.dt)
>>>     n = self.int_n(self.n, tdi.t, self.V, dt=tdi.dt)
>>>     V = self.int_V(self.V, tdi.t,  self.h, self.n, self.input, dt=tdi.dt)
>>>     self.spike.value = bm.logical_and(self.V < self.V_th, V >= self.V_th)
>>>     self.V.value = V
>>>     self.h.value = h
>>>     self.n.value = n
>>>     self.input[:] = 0.
>>>
>>> run = bp.dyn.DSRunner(HH(1), inputs=('input', 2.), monitors=['V'], dt=0.05)
>>> run(100)
>>> bp.visualize.line_plot(run.mon.ts, run.mon.V, legend='V', show=True)
```

The above example can also be defined with `brainpy.JointEq`.

```>>> import brainpy as bp
>>> import brainpy.math as bm
>>>
>>> class HH(bp.dyn.NeuGroup):
>>>   def __init__(self, size, ENa=55., EK=-90., EL=-65, C=1.0, gNa=35., gK=9.,
>>>                gL=0.1, V_th=20., phi=5.0, name=None):
>>>     super(HH, self).__init__(size=size, name=name)
>>>
>>>     # parameters
>>>     self.ENa = ENa
>>>     self.EK = EK
>>>     self.EL = EL
>>>     self.C = C
>>>     self.gNa = gNa
>>>     self.gK = gK
>>>     self.gL = gL
>>>     self.V_th = V_th
>>>     self.phi = phi
>>>
>>>     # variables
>>>     self.V = bm.Variable(bm.ones(size) * -65.)
>>>     self.h = bm.Variable(bm.ones(size) * 0.6)
>>>     self.n = bm.Variable(bm.ones(size) * 0.32)
>>>     self.spike = bm.Variable(bm.zeros(size, dtype=bool))
>>>     self.input = bm.Variable(bm.zeros(size))
>>>
>>>     # functions
>>>     derivative = bp.JointEq([self.dh, self.dn, self.dV])
>>>     self.integral = bp.ode.ExponentialEuler(derivative)
>>>
>>>   def dh(self, h, t, V):
>>>     alpha = 0.07 * bm.exp(-(V + 58) / 20)
>>>     beta = 1 / (bm.exp(-0.1 * (V + 28)) + 1)
>>>     dhdt = self.phi * (alpha * (1 - h) - beta * h)
>>>     return dhdt
>>>
>>>   def dn(self, n, t, V):
>>>     alpha = -0.01 * (V + 34) / (bm.exp(-0.1 * (V + 34)) - 1)
>>>     beta = 0.125 * bm.exp(-(V + 44) / 80)
>>>     dndt = self.phi * (alpha * (1 - n) - beta * n)
>>>     return dndt
>>>
>>>   def dV(self, V, t, h, n, Iext):
>>>     m_alpha = -0.1 * (V + 35) / (bm.exp(-0.1 * (V + 35)) - 1)
>>>     m_beta = 4 * bm.exp(-(V + 60) / 18)
>>>     m = m_alpha / (m_alpha + m_beta)
>>>     INa = self.gNa * m ** 3 * h * (V - self.ENa)
>>>     IK = self.gK * n ** 4 * (V - self.EK)
>>>     IL = self.gL * (V - self.EL)
>>>     dVdt = (- INa - IK - IL + Iext) / self.C
>>>
>>>     return dVdt
>>>
>>>   def update(self, tdi):
>>>     h, n, V = self.integral(self.h, self.n, self.V, tdi.t, self.input, dt=tdi.dt)
>>>     self.spike.value = bm.logical_and(self.V < self.V_th, V >= self.V_th)
>>>     self.V.value = V
>>>     self.h.value = h
>>>     self.n.value = n
>>>     self.input[:] = 0.
>>>
>>> run = bp.dyn.DSRunner(HH(1), inputs=('input', 2.), monitors=['V'], dt=0.05)
>>> run(100)
>>> bp.visualize.line_plot(run.mon.ts, run.mon.V, legend='V', show=True)
```
Parameters:
• f (function, joint_eq.JointEq) – The derivative function.

• var_type (optional, str) – The variable type.

• dt (optional, float) – The default numerical integration step.

• name (optional, str) – The integrator name.

• dyn_vars (optional, dict, sequence of ArrayType, ArrayType) –

__init__(f, var_type=None, dt=None, name=None, show_code=False, dyn_vars=None, state_delays=None, neutral_delays=None)[source]#

Methods

 `__init__`(f[, var_type, dt, name, show_code, ...]) `build`() `cpu`() Move all variable into the CPU device. `cuda`() Move all variables into the GPU device. `load_state_dict`(state_dict[, warn, compatible]) Copy parameters and buffers from `state_dict` into this module and its descendants. `load_states`(filename[, verbose]) Load the model states. `nodes`([method, level, include_self]) Collect all children nodes. `register_implicit_nodes`(*nodes[, node_cls]) `register_implicit_vars`(*variables[, var_cls]) `save_states`(filename[, variables]) Save the model states. `set_integral`(f) Set the integral function. `state_dict`() Returns a dictionary containing a whole state of the module. `to`(device) Moves all variables into the given device. `tpu`() Move all variables into the TPU device. `train_vars`([method, level, include_self]) The shortcut for retrieving all trainable variables. `tree_flatten`() Flattens the object as a PyTree. `tree_unflatten`(aux, dynamic_values) Unflatten the data to construct an object of this class. `unique_name`([name, type_]) Get the unique name for this object. `vars`([method, level, include_self, ...]) Collect all variables in this node and the children nodes.

Attributes

 `arguments` All arguments when calling the numer integrator of the differential equation. `dt` The numerical integration precision. `integral` The integral function. `name` Name of the model. `neutral_delays` neutral delays. `parameters` The parameters defined in the differential equation. `state_delays` State delays. `variables` The variables defined in the differential equation.