I have a problem where plot seems to run forever. At least for three

minutes.

octave 4.3.0+. Signal 1.3.2

A web example:

https://p5r.uk/blog/2009/filters-with-gnu-octave.html% The sampling frequency in Hz.

Fsam = 1500;

% Nyquist frequency, in Hz.

% The Nyquist frequency is half your sampling frequency.

Fnyq = Fsam/2;

% The cut-off frequency of your Low pass filter in Hz.

% This frequency must be greater than 0 and less than Fnyq.

Fc=1/4;

% Create a first-order Butterworth low pass.

% The returned vectors are of legth n.

% Thus a first order filter is created with n = 2.

[b,a]=butter(2, Fc/Fnyq);

% Create a 5 seconds signal with 3 components:

% a 1 Hz and a 200 Hz sinusoidal component and some gaussian noise.

t=0:1/Fsam:5;

x=sin(2*pi*t) + sin(2*pi*200*t) + randn(size(t));

% Apply the filter to the input signal and plot input and output.

y=filter(b,a,x);

plot(t, [x; y])

m1 = abs(fft(x));

m2 = abs(fft(y))

subplot(2,1,1); plot(m1); ## OK

subplot(2,1,2); plot(m2); ## OK

close

plot([m1;m2]); ## seems to hang forever

What am I doing wrong?

Tom Dean

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