Figure 2 not working

% Heat diffusion in one dimensional wire within the explicit FTCS method

clear;

% Parameters to define the heat equation and the range in space and time

D = 1*10^-4; % Heat Conductivity parameter in m2/s

K = 1*10^-4; % Heat Conductivity parameter in s^-1

L = 5.; % Total length in m

T = 43200.; % Final Time

% Parameters needed to solve the equation within the explicit method

Nt = 7200; % Number of time steps

Dt = T/Nt; % Time step

Nx = 51; % Number of space steps in m

Dx = L/(Nx-1); % Space step

b = 1-(2*D*Dt/Dx^2)- K*Dt; % beta parameter in the finite- difference implementation

% Remember that the FTCS method is stable for b=<1

disp(b);

% The initial condition: the initial temperature of the pipe

for i = 1:Nx+1

x(i) = (i-1)*Dx; % we also define vector x, due to the space discretization

u(i,1) = sin (pi*x(i));

end

% Boundary conditions: the temperature of the pipe at the boundaries at any time

for k =1:Nt+1

u(1,k) = 1.;

u(Nx+1,k) = 1.;

t(k) = (k-1)*Dt; % we also define vector t, due to the time discretization

end

% Implementation of the explicit FTCS method

for k =1:Nt % Time Loop

for i=2:Nx; % Space Loop

u(i,k+1) =u(i,k) + D*Dt/(Dx)^2*(u(i+1,k)-2*u(i,k)+u(i-1,k)); % Implementation of the FTCS Method

end

end

%Graphical representation of the temperature at different selected times

figure(1)

plot(x,u(:,1),'-b',x,u(:,round(Nt/100)),'--g',x,u(:,round(Nt/10)),':b',x,u(:,Nt),'-.r')

Title('Temperature of the pipe within the explicit FTCS method')

xlabel('X')

ylabel('T')

figure(2)

mesh(t,x,u)

title('temperature of the pipe within the explicit FTCS method')

xlabel('t')

ylabel('x')

I'm not able to get my mesh figure and im not sure what input should i give for this problem

[Torsten]

Didn't you read how to apply the mesh command ?

https://de.mathworks.com/help/matlab/ref/mesh.html

[Naveen Krish]

I read and im not sure what should i give in this part for my problem [X,Y] = meshgrid(-5:0.5:5)

[Torsten]

If you don't understand what to use as input to meshgrid, the usual next step is to look for meshgrid:

https://de.mathworks.com/help/matlab/ref/meshgrid.html

[Naveen Krish]

figure(2)

t = [2 4 6 8 10 12];

x = 1:5;

[t,x] = meshgrid(t,x)

mesh(t,x,u)

I used this for my figure 2 and it got blank

[Torsten]

  x = 0:0.1:1;
  y = 0:0.05:2;
  for i=1:numel(x)
    for j =1:numel(y)
      z(j,i) = x(i)^2 + y(j)^2;   
    end
  end
  [X,Y] = meshgrid(x,y);
  size(X)
  size(Y)
  size(z)
  mesh(X,Y,z)

Here you see that "mesh" works if the sizes of X,Y and z match.

Check the inputs in your case for their sizes and you'll see that they don't match.