Create a 3D Matric

Hello,

I'd like to create a 3D matrix which changes for each loop with the following code :

      X=ones(2*n+1,1);    
      for t=1:3
          B1=vertcat(zeros(n,1),X(n,1,t)*ones(n+1,1));
          X(:,:,t+1)=B1(:,:,t);
      end

And I keep having this mistake on the B2 line, saying the dimensions mismatch. I tried different things, but I don't understand why it doesn't work. Could anyone of you help me please ? Thanks a lot !

[M]

What do you want to do exactly ?

X should be a 3D matrix ? here you are defining vectors.

[Lucas Rauscher]

I'd like to implement my X matrix at the time t+1, according to the B matrix at the time t.

      X(:,:,4)=ones(2*n+1,1);    
      for t=1:3
          B1=vertcat(zeros(n,1),X(n,1,t)*ones(n+1,1));
          X(:,:,t+1)=B1(:,:,t);
      end

In that case X is a 3D matrix, but I still have a "index exceeds matrix dimensions" on this line :

X(:,:,t+1)=B1(:,:,t);

[M]

I guess your problem is for t>1 when you're trying to access B1(:,:,t), as B1 is a vector. Why would you want to access third dimension of B1 ?

[Stephen23]

Lucas Rauscher's "Answer" moved here:

Ok I'm sorry I'll explain what I try to achieve : The aim is to get Xsuiv(:,:,t), from t=1 to 10. So I initialize Xsuiv(:,:,1)=ones(NN,1);. Then, to get Xsuiv(:,:,t+1) I need to get Bsuiv(:,:,t). And to get Bsuiv(:,:,t) I can calculate it with Xsuiv(:,:,t-1) And once I have Bsuiv(:,:,t) I can get Xsuiv(:,:,t+1).

Xsuiv(:,:,1)=ones(N*M,1);

for t=2:10

Bsuiv=vertcat(zeros(n,1),Tp*ones(n+1,1));

for k=1:m-1
    Bsuiv=vertcat(Bsuiv,zeros(n+1,1));
    for i=1:n-1 
    %ERROR Bsuiv=vertcat(Bsuiv,((Xsuiv(k*N+n+i+1,1,t-1)-2*Xsuiv(k*N+n+i,1,t-1)+Xsuiv(k*N+n+i-1,1,t-1))
    end
    Bsuiv=vertcat(Bsuiv,Tp*ones(1,1));
end
Bsuiv=vertcat(Bsuiv,zeros(N,1));

Xsuiv(:,:,t+1)=eye(N*M,N*M)*Bsuiv(:,:,t);
end

Is it clear enough ? And one of my problems is to make Bsuiv a 3D matrix. For example in that case the line %ERROR is wrong because of the Xsuiv(...,...,t-1). But if I write

Bsuiv(:,:,t)=vertcat(Bsuiv,((Xsuiv(k*N+n+i+1,1,t-1)-2*Xsuiv(k*N+n+i,1,t-1)+Xsuiv(k*N+n+i-1,1,t-1))

it's still wrong

Answer 1

[Jan]

You want a 3D array. Then define a 3D array:

   X = ones(2*n+1, 1, 4);
   for t = 1:3
     B1         = vertcat(zeros(n,1), X(n,1,t) * ones(n+1, 1));
     X(:,:,t+1) = B1;
   end

It is strange, that you access X(n,1,t) before it was written. But because you have posted the failing code only, it is hard to guess, what you want to achieve. Add some explanations.