Subscripted assignment dimension mismatch - Help

 Hello everybody i have been trying to code a 1D wave problem using the Leap Frog Scheme but i am running into an error that i am not familiar with. Any suggestions?

freq = 1;                                        % Hz
omega = 2*pi*freq;                   % angular speed m/s
c = 10;                                           % m/s
amp = 1;
% Space
dx = 0.001;
xmax = 1;                                    % domain of unit length
lambda = 0.05;                          % size of wave
k = 2*pi/lambda;                      % wavenumber
x = 0:dx:xmax;
Vx = length(x);                         % matrix of propagation in the x direction
u_0 = zeros(size(x));

 % defining wave initial conditions 

for i = 1:Vx;
  if x(i) < lambda;
      u_0(i) = (1 - cos(k*x(i)))*0.5;
  else
      break
  end
end

 %Time
  dt = 0.01;
  t = 0:dt:1;
  Vt = length(t);

figure(1)
plot(x,u_0,'.-b');
axis([0 lambda 0 1])

phi = zeros(Vx,Vt);

for n = 1:Vx;
 phi(1,i) = u_0(i);
 phi(2,i) = u_0(i); 
end

 for i = 2:Vt
   for n = 2:Vx-1
      phi(i,n+1) = phi(i,n-1) + (u_0*(dt/dx))*(phi(i+1,n) - phi(i-1,n)/phi(i,n-1));
   end
 end

Answer 1

[Sean de Wolski]

It means you're trying to put more (or less) elements in a place than you've indexed.

%E.g.
A = [2, 3]
B = magic(3)
B(1,1:3) = A; %your error

What line does it say the error occurred on and what do you do for indexing at that line?

[Francis Mboya]

I understand the error now thanks.

Answer 2

[Walter Roberson]

In your line

phi(i,n+1) = phi(i,n-1) + (u_0*(dt/dx))*(phi(i+1,n) - phi(i-1,n)/phi(i,n-1));

u_0 is a vector, so the right hand side is going to have a vector result, which you then try to store in to a single memory location.

Perhaps your right hand side should use u_0(i) ?

[Francis Mboya]

Thanks Walter, worked like a charm!!! I have been working on this for a week now and i was clueless. kudos

[Francis Mboya]

Hello Walter, I was wondering if there is a way to make the wave plot figure(1) move across the domain till it reaches xmax? Thanks