diffusion with difference finite metod

Good morning.

I do not understand the error in this script:

param.Cafeed=0.014158;% concentration [mol/dm3]

param.v=0.1;

param.L=1.1245; % led leight [dm]

param.D=0.001;

nx = 100; % to define the dimension of the initial condition

x = linspace(0,param.L,nx);

h = x(2)-x(1);

y0 = zeros(nx,1);

y0(1) = param.Cafeed;% Boundary condition

tspan = linspace(0,30,nx);

[t,y] = ode15s(@(t,y)fun(t,y,param,h),tspan,y0);%To solve the time dependence

function dy=fun(t,y,param,h)

M = length(y)+1;

dy = zeros(M+1,1);

dy(1)= 0;

for i=2:M

dy(i) = -param.v*(y(i)-y(i-1))/h+(param.D/h^2*(-2*y(i)+y(i-1)+y(i+1)));

end

thank you

[Torsten]

1. You have M-1 unknowns y, but you try to provide M time derivatives dy.
2. You reference y(M) and y(M+1) in your loop which do not exist.
3. You have to prescribe a boundary condition at x=L. Open boundaries are not allowed for second-order PDEs.

Best wishes

Torsten.

Answer 1

[bianchi fiammetta]

Thank you.

[Torsten]

By the way:

This kind of equation can be solved using PDEPE.