I try to use Matlab to solve heat equation $$ \begin{cases} u_t-\Delta u=0 \\ u|_{t=0}=1-x^2-y^2 \\ u|_{\partial\Omega}=0\\ \Omega: x^2 + y^2 \le 1 \end{cases} $$ Pictures below is the parameter I using, but obviously, the result is wrong, since when $t=0$, the maximum of $u$ is $1$, but when $t=10$, the maximum of $u$ is bigger than $1$.
