Base ODE 2

The full solution can be found at basic_odes.ipynb.

Problem Setup

\[\frac{d x}{d t} = x, x(0)=1\]

The solution is \(x(t)=e^t\)

Implementation

1. Import necessary packages

   import os
   import numpy as np
   import torch
   import matplotlib.pyplot as plt
   from deep_macrofin import PDEModel
   from deep_macrofin import ActivationType, Comparator, EndogVar, EndogVarConditions, EndogEquation
   

2. Define problem
   Here, we use the default training configuration, and default setup for learnable endogenous variable.

   ode2 = PDEModel("ode2") # define PDE model to solve
   ode2.set_state(["t"], {"t": [-2., 2.]}) # set the state variable, which defines the dimensionality of the problem
   ode2.add_endog("x") # we use endogenous variable to represent the function we want to approximate
   ode2.add_endog_equation("x_t=x", label="base_ode") 
   ode2.add_endog_condition("x", 
                                 "x(SV)", {"SV": torch.zeros((1, 1))},
                                 Comparator.EQ,
                                 "1", {},
                                 label="initial_condition") 
   

3. Train and evaluate

   ode2.train_model("./models/ode2", "ode2.pt", True)
   ode2.eval_model(True)
   

4. To load a trained model

   ode2.load_model(torch.load("./models/ode2/ode2.pt"))
   

5. Plot the solutions

   fig, ax = plt.subplots(1, 3, figsize=(18, 6))
   t = np.linspace(-2, 2)
   ax[0].plot(t, np.exp(t), label="e^t")
   ax[1].plot(t, np.exp(t), label="e^t")
   ax[2].plot(t, np.exp(t), label="e^t")
   ode2.endog_vars["x"].plot("x", {"t": [-2, 2]}, ax=ax[0])
   ode2.endog_vars["x"].plot("x_t", {"t": [-2, 2]}, ax=ax[1])
   ode2.endog_vars["x"].plot("x_tt", {"t": [-2, 2]}, ax=ax[2])
   plt.subplots_adjust()
   plt.show()