For loop trouble!

What I am trying to do is, assume the first vector to be [1; 1; 1] and run the loop until difference in u is less than 0.0001. Before going into the loop, for some reason, I cannot set the first vector by saying u(1) = [1; 1; 1]

Here is what I have:

w = 100; 
gravity = 32.2*12; 
m = w/gravity;
k = 326.32;
K = [2 -1 0; -1 2 -1; 0 -1 1];
K = k*K
Kinv = inv(K)
M = [1 0 0; 0 1 0; 0 0 0.5];
M = m*M
u(1) = [1; 1; 1];
i = 1;
for i = 1:10;
    Mstar = u(i) * M * u(i)'
    Kstar = u(i) * K * u(i)'
    L(i) = Kstar(i) / Mstar(i)
    RHS = L(i) * M * u(i)'
    u(i+1) = Kinv * RHS(i)

      Diff = u(i+1) - u(i);
      if Diff > 0.0001;
          u(i+1) = u(i+1)
      else
          break
      end
  end

Answer 1

[Walter Roberson]

u(1) is a specific numeric array locations. Numeric array locations can only hold a single numeric value; you are trying to store three numeric values in that one location.

You probably just want

u = [1; 1; 1];

Answer 2

[Christoph F.]

I assume you want to keep the intermediate values of u?

In that case, use u(:, 1) = [1; 1; 1] (or u = [1; 1; 1]). Then you can access the i-th version of u with u(:, i).

However, you may want to initialize u as a matrix, to avoid time-consuming resizing of u in the loop. This can be done by initializing u with u = zeros(3, 11); u(:, 1) = [1; 1; 1];

Answer 3

[Andrei Bobrov]

w = 100; 
gravity = 32.2*12; 
m = w/gravity;
k = 326.32;
K = [2 -1 0; -1 2 -1; 0 -1 1];
K = k*K;
M = [1 0 0; 0 1 0; 0 0 0.5];
M = m*M;
u = [1; 1; 1];
for ii = 1:10;
    Mstar = u(:,ii)' * M * u(:,ii);
    Kstar = u(:,ii)' * K * u(:,ii);
    L = Kstar / Mstar;
    RHS(:,ii) = L * M * u(:,ii);
    u(:,ii+1) = K\RHS(:,ii);
    Diff1 = u(:,ii+1) - u(:,ii);
    if norm(Diff1) < 0.0001
        break
    end
end