, , 5 12 . - -:
>> t=0:0.001:2;
>> x=sin(2*pi*5*t)+cos(2*pi*12*t);
>> plot(t,x),grid;
>> title('input');
>> xlabel('t, c');
>> ylabel('X(t)')
>> y=fft(x);
>> a=abs(y);
>> plot(a);grid;
>> title('fourier');
>> xlabel('number');
>> ylabel('absF(X(t))')
ifft:
>> z=ifft(y);
>> plot(t,z), grid;
>> title('inverse');xlabel('number');
>> xlabel('t, c');
>> ylabel('Z(t))')
, .
(4) :
- m tm, x(m);
- k fk, y(k) ;
- , h , x(t), T , ;
Df=1/T,
F=1/h.
Df=0.5, F= 1000.
- - fft 0 F, ; , [-F/2 - F/2].
>> f=0:0.5:1000;
>> plot(f,a)'grid;
>> plot(f,a);grid;
>> title('F(x)');xlabel('friquency, Hz');
>> ylabel('abs(F(X))')
(5 12 ), .
y fftshift. z z
>> f1=-500:0.5:500;
>> v=fftshift(y);
>> a=abs(v);
>> plot(f1(970:1030),a(970:1030));grid;
>> title('F/N');
>> xlabel('friquency, Hz');
>> ylabel('abs(F(X))/N')
, - 5 12 .
, . , y N:
>> N=length(y);
>> a=abs(v)/N;
>> plot(f1(970:1030),a(970:1030));grid;
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>> title('F/N');
>> xlabel('friquency, Hz');
>> ylabel('abs(F(X))/N')