Subscripted assignment dimension mismatch - Help

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Francis Mboya
Francis Mboya 2011-4-12
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

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采纳的回答

Sean de Wolski
Sean de Wolski 2011-4-12
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?

更多回答（1 个）

Walter Roberson
Walter Roberson 2011-4-12
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) ?
  2 个评论
Francis Mboya
Francis Mboya 2011-4-12
Thanks Walter, worked like a charm!!! I have been working on this for a week now and i was clueless. kudos
Francis Mboya
Francis Mboya 2011-4-13
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

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