I have worked with MATLAB for calculating below equation for any time ($n$) and place($i$). In this equation, flux limiter is used.
$$C(i,n+1)=C(i,n)-V\left[1+\frac{1}{2}\psi(r_i)-\frac{1}{2}\frac{1}{(r_i-1)}\psi(r_i-1)\right]\left(C(i,n)-C(i-1,n)\right)$$
By writing the equation, the amount of flux limiter in the time zero ($n=0$) faced problem.
As you know, $r_i=\frac{C(i+1,n)-C(i,n)}{C(i,n)-C(i-1,n)}$, which the amount of $C$ in the time zero ($n=0$) for all places ($i$) is the same, then I reached undefined value ($0/0$) for $r$ in time zero($n=0$).
Is there any equation or any amount for calculating $r$ in the time of zero?