I know why the error is the zeroes?

clear all;
close all;
clc;
dt=0.25;
x=-40:450;
ui=0.5.*exp(-log(2).*(x./3).^2);
figure(1)
plot (x,ui)
xlabel('x-axis')
ylabel('u(x,0)')
xlim([-40 450])
ui=0.5.*exp(-log(2).*((x-400)./3).^2);
figure(2)
plot (x,ui)
xlabel('x-axis')
ylabel('u(x,400)')
xlim([350 450])
ylim([-0.2 0.6])
%%Central difference
unew=zeroes(1,471);
uold=ui;
for j=1:1600
    unew(1)=uold(1)-dt*((uold(2)-uold(1))/2);
    for i=2:length(ui)-1
        unew=uold(i)-dt*((uold(i+1)-uold(i-1))/2);
    end
    
    uold=unew;
    j*dt;
end

figure
plot(x,ui(x,400))
hold on 
plot(x,unew)
hold off 
title('central difference @dt=0.25')

[Star Strider]

Not spelled correctly. Should be:

unew = zeros(1,471);

[darova]

unew has no index?

unew=uold(i)-dt*((uold(i+1)-uold(i-1))/2);

Answer 1

[Hiroki Okawa]

1.

% unew = zeros(1,471);
unew = zeros(size(ui));

2.

% unew=uold(i)-dt*((uold(i+1)-uold(i-1))/2);
unew(i)=uold(i)-dt*((uold(i+1)-uold(i-1))/2);

3.

% plot(x,ui(x,400))
plot(x,ui)