Requirements of a program

• Compute the numerical solution $u^n$, $n=1,2,\ldots,N_t$
• Display the numerical and exact solution $\uex(t)=e^{-at}$
• Bring evidence to a correct implementation (verification)
• Compare the numerical and the exact solution in a plot
• computes the error $\uex (t_n) - u^n$
• computes the convergence rate of the numerical scheme
• reads its input data from the command line