Symplectic integrators of the pendulum equation?

In summary, velocity Verlet integration can be applied to generalized coordinates, as long as the acceleration term is calculated correctly.
  • #1
exmachina
44
0
In particular, a symplectic integrator to solve:

[itex]\ddot{\theta} + \dfrac{g}{l} \sin(\theta) = 0[/itex]

I'm currently using velocity verlet - by realizing that

[itex]\ddot{\theta} = -\nabla (-cos(\theta)) = A(\theta(t))[/itex]

ie. letting x = theta
v = dtheta/dt
a = d^2 theta /dt^2

is it safe to apply verlet integration to generalized coordinates? In particular, does this hold true for a generalized coordinate theta:

[itex]\theta_{t+dt} \approx \theta_t + \dot{\theta}_t dt + \frac{1}{2} \ddot{\theta}_t (dt)^2[/itex]
 
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  • #2
Yes, it is safe to apply velocity Verlet integration to generalized coordinates. This equation is the same as the one for theta. The only difference is that the acceleration term now depends on theta instead of a constant.
 

FAQ: Symplectic integrators of the pendulum equation?

What is a symplectic integrator?

A symplectic integrator is a numerical method used to solve differential equations, particularly those that describe physical systems. It preserves the important physical properties of the system, such as energy and momentum, and is often more accurate and efficient than traditional numerical methods.

What is the pendulum equation?

The pendulum equation is a second-order differential equation that describes the motion of a simple pendulum. It is given by d2θ/dt2 + (g/l)sin(θ) = 0, where θ is the angle of the pendulum, t is time, g is the acceleration due to gravity, and l is the length of the pendulum.

Why use a symplectic integrator for the pendulum equation?

The pendulum equation is a conservative system, meaning that energy is conserved. Traditional numerical methods can introduce errors that cause the energy of the system to increase or decrease over time. Symplectic integrators, on the other hand, preserve the energy of the system, making them a better choice for solving the pendulum equation.

What are the advantages of using symplectic integrators for the pendulum equation?

Aside from preserving the energy of the system, symplectic integrators also have better long-term stability and accuracy compared to traditional numerical methods. They can also handle stiff systems, such as the pendulum equation, more efficiently.

Are there any limitations to using symplectic integrators for the pendulum equation?

While symplectic integrators are generally more accurate and efficient for solving the pendulum equation, they may not work well for all types of differential equations. They are specifically designed for conservative systems, so they may not be the best choice for non-conservative systems. Additionally, the choice of integrator and the step size may affect the accuracy and stability of the solution.

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