Undefined function or method 'fft' for input arguments of type 'sym'.

Hi Everyone: When I run this script:

syms t

x=-3:.1:3;

for i=1:length(x);

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

    z=x(i);

    Eo(i)=int(Pin,t,-inf,z);

    Ein(i)=int(Pin,t,-inf,inf);

    E(i)=Eo (i)/Ein(i);

    Go=1000;

    G(i)=Go/(Go-(Go-1)*exp(-E(i)*0.1));

    Pin=3*exp(-x(i)^2);

    Pout(i)=Pin*G(i);

    Poutf=fftshift(fft(Pout,100000));

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

end

plot(f,abs(Poutf),'-r*')

I face this error:

Undefined function or method 'fft' for input arguments of type 'sym'.

Could anyone help me please?

Answer 1

[Wayne King]

fft is not overloaded for symbolic inputs. fft() is only for numeric inputs. If you want the Fourier transform of a symbolic input, see fourier

Answer 2

[Walter Roberson]

Use E(i) = double(Eo (i)/Ein(i));

Note: it is a waste of time to do the integrations ever iteration. Do the integration with a symbolic upper bound once before the loop, evaluate that with infinity as the upper bound once before the loop to get the constant Ein, and then in your loop subs() your x(i) in to the indefinite integral as the upper bound to get Eo(i).

The ratio will, by the way, come out as (1+erf(x(i))/2