Struggling with array dot operator

I've initialized

t = 0:0.1:20;
L = zeros(4,4,length(t));

I'm trying to assign values to L as follows:

t=0:0.1:20;

for i =1:length(t),

L(:,:,i) = D*diag([(t.^2+1).^2*(sin(t).^2), (t.^2+1).^2*(sin(2*t).^2), (t.^2+1).^2*(sin(3*t).^2), (t.^2+1).^2*(sin(4*t).^2), (t.^2+1).^2*(sin(5*t).^2)])*D';

end

D is a constant matrix. Essentially, there is a different L for each time instant. When I execute this, it gives

Error using  * 
Inner matrix dimensions must agree.

I'm tried so many combinations of the dot operators since this is a long operation.

Can someone help identify the problem?

Thanks a lot.

Answer 1

[Matt J]

Define the t-data before the for loop

    T=0:0.1:20;
    for i =1:length(T),
     t=T(i);
  L(:,:,i) = D*diag([(t.^2+1).*(t.^2+1).*(sin(t).^2) (t.^2+1).*(t.^2+1).*
(sin(2*t).^2) (t.^2+1).*(t.^2+1).*(sin(3*t).^2) (t.^2+1).*(t.^2+1).*(sin(4*t).^2) 
(t.^2+1).*(t.^2+1).*(sin(5*t).^2)])*D';

end

Also, it is a good ideas to use commas to explictly separate entries of a vector/matrix.

[Deepayan Bhadra]

Hi Matt, I've made the question more compact but the error persists since it seems not because of 't' definition but rather due to dot array multiplication. Could you check that? Thanks.

[Matt J]

What are the dimensions of D?

[Matt J]

This works for me, if D is 5x5,

    T=0:0.1:20;
    for i =1:length(T),

      t=T(i);

L(:,:,i) = D*diag([(t.^2+1).*(t.^2+1).*(sin(t).^2),...
                   (t.^2+1).*(t.^2+1).*(sin(2*t).^2),...
                   (t.^2+1).*(t.^2+1).*(sin(3*t).^2),...
                   (t.^2+1).*(t.^2+1).*(sin(4*t).^2),... 
                   (t.^2+1).*(t.^2+1).*(sin(5*t).^2)])*D';

   end

[Deepayan Bhadra]

This is working now :) Thanks!

Answer 2

[Walter Roberson]

In the computation for L you should be using t(i) not t