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0 < Xo,Yo < 250.
The script makes 2 it iterations with the time steps
Δt = 0.05 per frame. Set it = 1 and γ = 0
after you get a stationary pattern. Two degenerate eigenmodes
u_{5,7} and u_{7,5} are exited.
Set X_{o} = 100 to see only one mode.
If you are bored of watching relaxation try the
Square wave eigenmodes script.

Resonance

A CPU based simulation of the wave equation with time periodic perturbation
∂_{t}^{2}u +
γ∂_{t }u = Δu + f_{o}
δ(r - r_{o }) sin ωt,
where γ is small damping (diffusion).
Simple explicit scheme on a 250x250 grid is used. It is stable for
the time steps Δt < h, where h = π/(N-1) is the
space step of the grid.
For the square membrane wave eigenmodes and eigenfrequencies are
u_{n,m} = sin(nx) sin(my)
sin(ω_{o }t),
ω_{o}^{2} = n^{2} + m^{2}. You can see that in resonance ω = ω_{o}
(and γ = 0) wave amplitude increases to infinity.