I keep getting this matrix error when I run my code, any tips how I can fix it, its line 45.

N=10;
L=10;
D=.01;
dt=.01;
k_on=1;
k_off=.1;
F=1;
tmax=100;

x=L*rand(N,1);
y=L*rand(N,1);
state=zeros(N,1);

figure;
axis([0 L 0 L]);
set(gca,'nextplot','replacechildren');

for t = 0:dt:tmax
    dx=sqrt(2*D*dt)*randn(N,1);
    dy=sqrt(2*D*dt)*randn(N,1);

    x=x+dx;
    y=y+dy;

    x(x<0)=0;
    x(x>L)=L;
    y(y<0)=0;
    y(y>L)=L;
    p_on=k_on*dt*F;
    p_off=k_off*dt;

    for i = 1:N
        if state(i)==0
            if rand < p_on
                state(i)=1;
            end
        else
            if rand<p_off
                state(i)=0
            end
        end
    end
colors= repmat([1 0 0], N,1)
colors(state == 1,:,:) = repmat([0 1 0],sum(state),1);
scatter(x,y,50,colors,'filled');
title(sprintf('Time=%.2f',t));
drawnow;
if any(state == 1)
    p_bind=1-exp(-k_on*dt*F);
    if rand<p_bind
        [~,i]=max(state);
        state(i)=2;
        colors(i,:)=[0]
       
    end
end
end

Unable to perform assignment because the size of the left side is 8-by-3 and the size of the right side is 10-by-3.

colors(state == 1,:,:) = repmat([0 1 0],sum(state),1);

Answer 1

[DGM]

The error says it all. You're indexing the LHS based on state == 1. You're generating the RHS based on the sum of state. State contains values other than [0 1], so sum(state) is not necessarily equal to sum(state==1).