FDTD algorithm in Ruby

fdtd.rb

include Math
require 'pp'

X = 10
T = 4
PI = 3.14

dt = 1
dx = 1

# HW4 prob.2
#V = 0.8
#psi = [
#  [0, 0, Math.sin(PI/4), sin(2*PI/4), sin(3*PI/4), 0, 0, 0, 0, 0, 0],
#	[0, 0, Math.sin((1-0.8)*PI/4), sin((2-0.8)*PI/4), sin((3-0.8)*PI/4), sin((4-0.8)*PI/4), sin((5-0.8)*PI/4), 0, 0, 0, 0],
#]
#def s(x,t); 0; end

# HW6 problem3
V = 0.5
psi = [ [0]*X ]
def s(x,t)
	if x == 5 && t == 0
		1
	else
		0
	end
end

(psi.size-1).upto(T-1) { |t|
	psi[t+1] = []
	0.upto(X-1) { |x|
		right = x == X-1 ? 0 : psi[t][x+1]
		left = x == 0 ? 0 : psi[t][x-1]
		old = t == 0 ? 0 : psi[t-1][x]
		
		psi[t+1][x] = -old + 2*psi[t][x] + V*V*dt*dt/dx/dx * (left + right - 2*psi[t][x]) + dt*dt*s(x,t)
	}
}

pp psi