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

Hi every body,

When I run this code:

t=-3:.1:3;

Go=1000;

Bc=5;

Pin=@(t)3*exp(-t.^2);

Ein = quadgk(Pin,-inf,inf);

for m=1:length(t);

        z=t(m); 

        E1=quadgk (Pin,-inf,z)/Ein; 

        G(m)=Go/(Go-(Go-1)*exp(-E1*0.1));

        Pout(m)=Pin(z)*G.*1; 

        Phi(m)=-0.5*Bc*log(G.*1);

        Aout(m)=sqrt(Pout)*exp(i*Phi);

end

Aoutf=fftshift(fft(Aout,100000));

f = -(-100000/2:(100000/2-1)).*1/(0.01*100000);

Poutf = abs (Aoutf).^2;

plot(f,Poutf,'--')

xlim([-15 5])

I face this error:

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

Please help me, and thanks all in advance

Answer 1

[Matt Tearle]

G is growing in the loop, so Pin(z)*G is a vector (for m >= 2). You can't assign a vector to the single value Pout(m), hence the error.

Perhaps you mean Pout(m) = Pin(z)*G(m)?

Also, you should preallocate these arrays, so they don't grow inside the loop:

tlen = length(t);
G = zeros(1,tlen);
Pout = zeros(1,tlen);
etc

EDIT TO ADD: Actually, assuming you are just trying to do element-by-element calculations here, you don't need to do all these in the for loop. The quadrature is the only thing that needs a loop, so try this:

t=-3:.1:3;

Go=1000;

Bc=5;

Pin=@(t)3*exp(-t.^2);

Ein = quadgk(Pin,-inf,inf);

for m=1:length(t);
    z=t(m);
    E1=quadgk (Pin,-inf,z)/Ein;
end

G=Go./(Go-(Go-1)*exp(-E1*0.1));
Pout=Pin(t).*G.*1;
Phi=-0.5*Bc*log(G.*1);
Aout=sqrt(Pout)*exp(1i*Phi);

Aoutf=fftshift(fft(Aout,100000));

f = -(-100000/2:(100000/2-1)).*1/(0.01*100000);

Poutf = abs (Aoutf).^2;

plot(f,Poutf,'--')

xlim([-15 5])

[Abdulaziz]

Thanks a lot Matt Tearle