found unsupported dynamic matrix type at output port 0

hi. I am working on Fast Fourier transform here i am converting FFT into HDL code. While converting i am getting error " Found unsupported dynamic matrix type at output port :0 i.e is z. My code is as below

function z=Fast_Fourier_Transform(x,nfft)
N=length(x);
z=complex(zeros(1,nfft));
Sum=complex(0);
for k=1:nfft
    for jj=1:N
        a=-2*pi*(jj-1)*(k-1)/nfft;
        a1=cos(a)+1j*sin(a);
        Sum=Sum+x(jj).*a1;

      end
  z(k)=Sum;
  Sum=0;% Reset
  end
  return

testbench:
Fs = 150; % Sampling frequency
t = 0:1/Fs:1;
f = 5;
nfft = 1024; 
x= cos(2*pi*t*f);
z=Fast_Fourier_Transform(x,nfft);
z = z(1:nfft/2);
mx = real(z);
% Frequency vector
f = (0:nfft/2-1)*Fs/nfft;
% Generate the plot, title and labels.
figure(1);
plot(t,x);
title('Sine Wave Signal');
xlabel('Time (s)');
ylabel('Amplitude');
figure(2);
plot(f,mx);
title('Power Spectrum of a Sine Wave');
xlabel('Frequency (Hz)');
ylabel('Power');

In workflow advisor i am getting error at last point i.e near hdlcode generation step. code is not reaching at this point and error is at same place

for jj=1:N
        a=-2*pi*(jj-1)*(k-1)/nfft;
        a1=cos(a)+1j*sin(a);
        Sum=Sum+x(jj).*a1;

      end

I am unable to debug this error please do help for my further process. THANK YOU

Answer 1

[Walter Roberson]

Remember that HDL is dealing with hardware. There is no memory allocation. Every array has to have a fixed maximum size so that the HDL process can generate enough hardware memory cells. If you invoke the routine multiple times with different nfft then code in the largest of the nfft as the maximum size. I believe you would do that using coder.varsize()

What I do not know at the moment is whether there is a way to configure the maximum size through a Constant Block or similar, to allow it to be a parameter of the system as a whole.

Answer 2

[Tim McBrayer]

The size of z is clearly dependent on the value of an input variable:

 z=complex(zeros(1,nfft));

Try it with an actual constant instead of nfft, and see how it goes.

[Amruta Radder]

Thank you.. I did with it

[Keerthi Venkat Reddy Mokka]

can you please tell me... what are the changes you did in your code?