# Tag Info

3

The choice of $k$ is restricted also by the discretization of the source term. To see it, rewrite your scheme to \begin{equation} u_m^{n+1} = \left(1 - \frac{k(1-x_m)}{h} - k(1-x_m)\right) u_m^n + \frac{k (1-x_m)}{h} u_{m+1}^n \,. \end{equation} You need $$1 - \frac{k(1-x_m)}{h} - k(1-x_m) \ge 0$$ for all $x_m$. Taking $x_m=0$ (the worst case scenario) you ...

2

I've identified a few "problems": Your analytical solution isn't quite correct. The correct analytical solution to the "infinite domain" advection equation is supposed to be $u(t,x) = u_0(x-at)$. Because you have periodic boundaries, you need to properly account for this by making sure $x-at$ is properly wrapped. I replaced your ...

1

I found a few issues with your implmentation: you should replace $t$ by $dt$ in your discrete equation (both in your code and in the question), otherwise it makes no sense ! the second part of your equation (with $a$) seems incomplete or wrong, and there's a mix between $F$ and $f$. Moreover, you flux evaluation is wrong: Fplus should read 0.5*Up**2 for ...

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