Why is my error not exactly 0

I wrote a very simple upwind difference scheme for the equation with , but for some reason the error is not exactly 0.

%u_t+u_x=0
space=[0.01,0.005,0.0025,0.00125];
error=zeros(size(space));
for j=1:size(space,2)
    dx=space(j);
    dt=dx;
    u=sin(0:dx:1);
    n=size(u,2);
    T=1/dt;
    for i=1:1
        ul=[sin(-dx-dt*(i-1)),u(1:(n-1))];
        u=(1-dt/dx)*u+ul*dt/dx;
    end
    error(j)=norm(u-sin((0:dx:1)-dt),1)/n;
end

Answer 1

[Image Analyst]

error is a built-in function. You must not use it as a name for your variable.

Does the FAQ answer your question?

https://matlab.fandom.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_(or_similar)_not_equal_to_zero?