A symplectic integrator is a tool that helps people who like to play with simulations to make their simulations more accurate. It's like a calculator, but instead of adding and subtracting numbers, it uses math to help simulate things like how planets move around the sun or how particles interact with each other.
The special thing about a symplectic integrator is that it helps maintain what's called "symplectic geometry," which means that the equations that describe how things move around in the simulation remain as close as possible to the original equations that were used to create the simulation. This is important because if the equations get really far away from those original ones, the simulation can stop being accurate and start giving answers that make no sense.
To help maintain this symplectic geometry, the symplectic integrator does some fancy math behind the scenes that involves breaking down each step of the simulation into tiny pieces and figuring out exactly how to move things around during each step in a way that keeps the simulation on track. It's like taking small steps on a tightrope to keep your balance, rather than trying to take big leaps and risking a fall.
People who use symplectic integrators often use them to simulate things like the motion of planets or particles in a physics experiment. By using these tools, they can simulate the motion of the objects with great precision, which can help them understand how different things behave under different conditions.