Residual vs Iteration Plot

I'm trying to plot the convergence of when the residual reaches 1e-5 after a certain number of iterations. My figure(1) plot is weird, and doesn't plot a line showing its convergence over the iteration interval. It kind of plots the axes at a specific point, with no line. Please help.

L = 0.05;                                                               
T_w = 5;                    
T_e = 100;                  
dx = 0.005;                
dy = dx;             
nx = (L/dx)+1;       
ny = nx;     
T = T_e*ones(nx,ny); 
eq_no = zeros(nx,ny);
max_iter = 10000;          % Maximum Iterations
max_res = 1e-5;             % Maximum Residual

for n = 1:max_iter
    Tn = T;                 % Previous Nodal Temperature (degC)
    for i = 1:nx
        for j = 1:ny
            if (i > 1 && i < nx && j > 1 && j < ny)
            eq_no(i,j) = 1;
            T(i,j) = (Tn(i,j+1) + Tn(i,j-1) + Tn(i+1,j) + Tn(i-1,j))/4;
            
            else
            eq_no(i,j) = 2;
            T(i,j) = T_w;
            
            end
        end
    end
      
    res = max(abs(T-Tn));
    if res < max_res
        break
    end
end

figure(1)
plot(n,res)
grid


figure(2)
pcolor(T')
shading interp
title('Nodal Temperature Distribution');
xlabel('Horizontal Nodes');
ylabel('Vertical Nodes');
colorbar();

Answer 1

[Mathieu NOE]

hello

code fixed :

L = 0.05;                                                               
T_w = 5;                    
T_e = 100;                  
dx = 0.005;                
dy = dx;             
nx = (L/dx)+1;       
ny = nx;     
T = T_e*ones(nx,ny); 
eq_no = zeros(nx,ny);
max_iter = 10000;          % Maximum Iterations
max_res = 1e-5;             % Maximum Residual
for n = 1:max_iter
    Tn = T;                 % Previous Nodal Temperature (degC)
    for i = 1:nx
        for j = 1:ny
            if (i > 1 && i < nx && j > 1 && j < ny)
            eq_no(i,j) = 1;
            T(i,j) = (Tn(i,j+1) + Tn(i,j-1) + Tn(i+1,j) + Tn(i-1,j))/4;
            
            else
            eq_no(i,j) = 2;
            T(i,j) = T_w;
            
            end
        end
    end
      
    res(n) = max(abs(T-Tn),[],'all'); % <= correction here 
    if res(n) < max_res
        break
    end
end
figure(1)
plot(1:n,res) % <= correction here
grid
figure(2)
pcolor(T')
shading interp
title('Nodal Temperature Distribution');
xlabel('Horizontal Nodes');
ylabel('Vertical Nodes');
colorbar();

[Sam McMillan]

Thank you, this was very helpful :)

[Mathieu NOE]

my pleasure !