How would you describe the Galerkin method to solving the 3D wave equation $$u_{tt}= c^2\Delta u$$ to someone who wants to implement it immediately?
More precisely, we want to solve the Cauchy problem $$u_{tt}= c^2\Delta u , \\ u_t(x,y,z,0)= g(x,y,z) , \\ u(x,y,z,0)= f(x,y,z)$$ where $f, g$ are given compactly supported functions.
Say in a bounded region of the space we are interested in, say a ball of radius $R$, note that the wave propagates towards the boundary of the region, the sphere, thus we can't impose the condition at the boundary.
How would you implement this method ? I am looking for a description of the finite elements, how to decompose this region? (you can use any other shape, not necessarily a ball, take a cube for example), then describing the numerical algorithm necessary to find the values of the solution $u$ at certain element or node $(x,y,z,T)$ at time $T$