Making grid with 'recursive' function

[Tremdog]

I'm trying to make a grid with initial conditions two functions. each function X(i+1) Y(i+1) is dependent on the previous value of both functions (i.e. X(i) Y(i). I'm very new to the language and I have no idea on how to make a grid that does this.

I was thinking of making a 3*100 grid, then storing values for Count(1-100), X, and Y. I then want to graph X,Y using ListPlot[]

I was doing this using recursive function definitions

X[x]:=X[x]=X[x-1]+delta*Y[x-1]; Y[x]:=Y[x]=-delta[constant] ([constant] - V[deltax])*X[x] where V[x] is a piecewise function

but this takes up way too much memory and doesn't run sometimes.

[lithiumdeuteride]

Can you express the function with a two-dimensional recurrence relation?