subscripted assignment dimension mismatch. for loop

In my code, i need to update the value of A with the calculated value C, but its not working The code is:

clc

clear

A=[1 0 1 0;0 1 0 1;0 0 1 0;0 0 0 1];

B=[1;-1;-0.05;0.05];

for i=1:10

C(i)=A*B

%update value

A=C(i)

end

[M]

What is the expected result ?

Answer 1

[Guillaume]

It's really not clear what you want to do. There are many issues with the short bit of code you've shown:

• Issue 1: What is the point of the loop? You have

for i = 1:10
  something = A*B
end

Nothing in the loop depends on i. Hence you're basically doing the exact same thing 10 times, each time completely overwriting what was calculated the previous step.

• Issue 2: Trying to assign a vector to a scalar

C(i) = A*B;

A*B is a 4x1 vector. Unless C is some obscure class, C(i) is a 1x1 scalar. You can't stuff 4 elements in a single slot. That's why you get the subscripted assignment dimension mismatch error. It's unclear what you're really trying to do here.

• Issue 3: Your update completely overwrite the whole of A

A = C(i);

As said, I'm not sure what you wanted C to contain. C(i) is scalar, but maybe you wanted it to contain the 4x1 vector. Either way, you're replacing a 4x4 matrix by either a 1x1 or a 4x1 array. There's no update there.