**theta_method**,
a Python code which
solves one or more ordinary differential equations (ODE)
using the theta method, and using a fixed time step.

The theta method uses a parameter theta, between 0 and 1. Special values of theta are:

- theta = 0: backward Euler method;
- theta = 1/2: trapezoidal method;
- theta = 1: forward Euler method;

The computer code and data files described and made available on this web page are distributed under the MIT license

**theta_method** is available in
a MATLAB version and
a Python version.

backward_euler, a Python code which solves one or more ordinary differential equations (ODE) using the backward Euler method.

backward_euler_fixed, a Python code which solves one or more ordinary differential equations (ODE) using the (implicit) backward Euler method, using a fixed point iteration for the implicit equation.

bdf2, a Python code which solves one or more ordinary differential equations (ODE) using BDF2, the (implicit) backward difference formula of order 2, using fsolve() to solve the implicit equation.

cauchy_method, a Python code which solves one or more ordinary differential equations (ODE) using the Cauchy method.

euler, a Python code which solves one or more ordinary differential equations (ODE) using the forward Euler method.

leapfrog, a Python code which uses the leapfrog method to solve a second order ordinary differential equation (ODE) of the form y''=f(t,y).

midpoint, a Python code which solves one or more ordinary differential equations (ODE) using the (implicit) midpoint method.

midpoint_adaptive, a Python code which solves one or more ordinary differential equations (ODE) using the (implicit) midpoint method, relying on fsolve() to solve the implicit equation, and using an adaptive timestep.

midpoint_explicit, a Python code which solves one or more ordinary differential equations (ODE) using the (explicit) midpoint method, also called the modified Euler method.

midpoint_fixed, a Python code which solves one or more ordinary differential equations (ODE) using the (implicit) midpoint method, using a simple fixed-point iteration to solve the implicit equation.

rk4, a Python code which applies the fourth order Runge-Kutta (RK) algorithm to estimate the solution of an ordinary differential equation (ODE).

rkf45, a Python code which implements the Runge-Kutta-Fehlberg ODE solver.

trapezoidal, a Python code which solves one or more ordinary differential equations (ODE) using the (implicit) trapezoidal method.

trapezoidal_fixed, a Python code which solves one or more ordinary differential equations (ODE) using the (implicit) trapezoidal method, using the fixed point method to handle the implicit system.

velocity_verlet, a Python code which uses a version of the velocity Verlet method to solve a secord order ordinary differential equation (ODE) of the form y''=f(t,y).

- theta_method.py, calls all the tests.
- theta_method.sh, runs all the tests.
- theta_method.txt, the output file.

- stiff_theta_method_0.png, an image of the solution for theta = 0.
- stiff_theta_method_0.5.png, an image of the solution for theta = 0.5.
- stiff_theta_method_1.png, an image of the solution for theta = 1.