Memory-saving implementation

• Note 1: we store the entire array u, i.e., $u^n$ for $n=0,1,\ldots,N_t$
• Note 2: the formula for $u^{n+1}$ needs $u^n$ only, not $u^{n-1}$, $u^{n-2}$, ...
• No need to store more than $u^{n+1}$ and $u^{n}$
• Extremely important when solving PDEs
• No practical importance here (much memory available)
• But let's illustrate how to do save memory!
• Idea 1: store $u^{n+1}$ in u, $u^n$ in u_1 (float)
• Idea 2: store u in a file, read file later for plotting