How do I fix this error: In an assignment A(I) = B, the number of elements in B and I must be the same!!!

Hi all,

I am very new to Matlab and I am trying to define a variable V to be any number >=700 within the following for loop:

    for i = 1:29   
    disp(i) = norm([p1(1,i+1),p1(2,i+1)]-[p1(1,i),p1(2,i)])*1000;
    V = randn(1x29);
    v >= 700;
    CL(i) = (W(i).*g)./(0.5*density*(V.^2)*S);
    CD(i) = CDo + ((CL(i).^2)/(3.14*AR*e));
    T = ((CD(i)/CL(i))*(W(i)*g))/1000;   
    Wf(i) = SFC*T*(disp(i)/V);
    W(i+1) = W(i)-Wf(i);
    end

I have tried defining V to be a random (1x29) matrix but I get the following error:

In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in trial (line 38)

    CL(i) = (W(i).*g)./(0.5*density*(V.^2)*S);

Can anybody please help?

Answer 1

[Image Analyst]

CL(i) is a single number, the i'th element of CL. You're trying to stuff a whole 29 element array into a space that can hold only a single number. Perhaps you want this???

CL(i) = (W(i).*g)./(0.5*density*(V(i).^2)*S);

If g, density, and S are also arrays, then you'd need to add (i) following them also, as well as having .* in front of S(i).

[Zena Assaad]

No I only want V to be a single number >= 700. How can I do that?

[Image Analyst]

To get a single number between 700 and some other number vLast, use rand(1)

V = 700 + (vLast-700)*rand(1);

and get rid of those two other lines you had for V.

[Zena Assaad]

This worked perfectly. Thank you very much!!!!!!

[Image Analyst]

You're welcome. Could you go ahead and officially mark the answer as "Accepted" then? Thanks in advance.