Tridiagonal Matrix for Lax friedrich scheme

Hello everyone, recently I tried writing the advection equation using both explicit (First order upwind) and implicit (TDMA) method. In which I was successfully able to run without any error for both methods. Please find attached code.

Currently I am trying to apply the same for 1D inviscid euler equation using Lax friedrich method. I was successfully able to code explicit method but for implicit I am unable to form the tridiagonal form for Lax friedrich method can anyone please help me here.

Laxfriedrich method: Newsolution=0.5*ui+1+0.5*ui-1-r*Fi+1+r*Fi-1; Where r is dt/(2*dx).

Thanks in advance.