By using only this input, z(n); how could I calculate the output by using filter command in matlab.
MATLAB: Filter command in matlab with only input system
filterinputMATLABoutput
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I hope this will be of some help.
b = [1, -.5]; a = [-.5, 1]; H= zplane(b,a);From your description it sounds like you are not also zero-ing out the complex conjugates. You are zero-ing out only the "positive" frequencies, but you also have to zero the corresponding negative frequencies. I'll illustrate this in the following example with two sine waves in noise. I'll remove the 200-Hz sine wave.
t = 0:0.001:1-0.001; x = cos(2*pi*100*t)+cos(2*pi*200*t)+randn(size(t)); % get rid of the 200-Hz component.
xdft = fft(x); % 200 Hz lives at bin 201
xdft(201) % but look at bin length(x)-201+2
xdft(length(x)-201+2)You see the difference between those is that one is the complex conjugate of the other. You have to zero them both.
xdft([201 length(x)-201+2]) = 0; xrec = ifft(xdft); plot(abs(fft(xrec)))You see now that the 200-Hz component is gone.
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