I am plotting the fft of the the raw data and when i change the N size the error ' Subscripted assignment dimension mismatch' shows up

Dear all i am trying to plot the FFT spectrum of the raw data in a for loop. The loop runs great when i run it at N=6554 and sampling frequency as 50e4 but when i change the N size to 655 i have this strange error. I dont think it might be due to the excess data size but I assume it might be with the loop but a bit confused in solving it. Would be glad if someone could help me with a suggestion or tip...Thank you

Fs=500000;

N=input('N='); %%adjusts delta-f and it adjusts the time interval for the single FFT spectrum

k=1;

f_start=input('f_start=');

overlap=input('Overlap factor=');

f_stop=input('f_stop=');

for i=f_start:overlap:f_stop-N

x(:,k)=abs(fft(Psign(i:i+N))); %%abs value of the FFT of the time domain signal

k=k+1;

end

p=20*log10(x(2000:N/2,f_start:f_stop)); %%conversion to dB scale

image(p) %%plots surface of the spectrum

figure

plot(p)

figure

plot(filter(ones(1,10)/10,1,p))

Answer 1

[Image Analyst]

In the statement

x(i,k)=abs(fft(Psign(i:i+N)));

x(i, k) is a single element, a single number. You are trying to assign a vector of many elements into that single element. You can't do that. It can take only 1 number, not hundreds.

[Image Analyst]

How many rows does x have? Are there N+1 rows in x, because that's what you're trying to put in there?