Matrix dimensions do not match

Hi, I am using the ode 45 function in matlab for my statespace model. For the last line of the code i keep getting the error In an assignment A(I) = B, the number of elements in B and I must be the same. This is for the line u(i)=(sin(f*2*pi.*t+(alpha(i)/2)))+(sin(f*2*pi.*t-(alpha(i)/2))); I thought i already assigned the matrix sizes in the lines above. what is the problem

u=zeros(1,8000);
  alpha=zeros(1,8000);
  [t,x]=ode45(@ssmodel,t,x0);

    for i=2:tstop*fsamp
        %u is the input,pout is the output power which is state variable x5 
        %squared over Resistance
        u(i)=u(i-1);
        pout=(x(:,5).^2)/Rac;
        %poutmean is just the average of pout
        poutmean(i)=((i-1)/i)*mean(pout(i-1,1))+ (pout(i,1))/i;

        %the error is fed to a PI controller, Kp is the proportional gain and 
        %Ki is the integral gain
        e(i)=pref-poutmean(i); 
        alpha(i)=((Kp+Ki)*e(i))-(Kp*e(i-1))+(alpha(i-1));

        %a limiter which limits the range of alpha to +-pi.
    if(alpha(i)>pi)
        alpha(i)=pi;

    else if (alpha(i)<-pi)
            alpha(i)=-pi;
        end
    end

    u(i)=(sin(f*2*pi.*t+(alpha(i)/2)))+(sin(f*2*pi.*t-(alpha(i)/2)));}

Answer 1

[Geoff]

You are calling sin() on an array. It returns an array. You are assigning that array to u(i), which is a single value in an array. You will get an error if you do that.

Also, don't use 'else if', use 'elseif' with one 'end'.

[Srikanth]

thanks for the reply, i am a little confused with the syntax. I want to pass each element of the array for alpha into the sin(), so i get the array for u updating for each increment of i. What is it that i am doing wrong here. I thought to assign it as a vector we just write u(i) in matlab script.