Oscilator - Using generated code

It might be beneficial to generate the C++ code first using the gotran2goss script in the CLI, and then use that code as input to the model. One advantage of this is that you can edit the C++ code directly before passing it to goss. This might be desirable if you want to implement logic into the model that is difficult to describe using gotran or if you want to bring in some third party library

As before we first need to import the necessary libraries

import goss
import matplotlib.pyplot as plt
import numpy as np

We assume that we ran the script

goss gotran2goss oscilator.ode

which produced the file oscilator.h. Inside this file there will be a method looking something like this

extern "C" DLL_EXPORT goss::ParameterizedODE * create_Oscilator()
{
  return new goss::Oscilator;
}

This is the method that will create the class that is exported to the python interface. Note that the method is called create_Oscilator, but if you try to use a different ode-file the name might be different, but it will always be create_{modelname}. This name needs to be provided as a keyword argument to the constructor, so that in our case we will have

oscilator = goss.ParameterizedODE("oscilator.h", name="Oscilator")

Next we create a solver

solver = goss.solvers.ThetaSolver(oscilator)

solve the system

u0 = oscilator.get_ic()
dt = 0.01
t = np.arange(0, 10 + dt, dt)
u = solver.solve(t, y0=u0)
u_exact = np.array([np.cos(t), np.sin(t)])

an finally plot the solution

fig, ax = plt.subplots()
ax.plot(t, u[:, 0], label="u1 (computed)")
ax.plot(t, u[:, 1], label="u2 (computed)")
ax.plot(t, u_exact[0, :], label="u1 (exact)", linestyle="--")
ax.plot(t, u_exact[1, :], label="u2 (exact)", linestyle="--")
ax.legend()
plt.show()

Fig. 4 Computed and exact solution of the oscilator ODE.