add an iirFIlter function to choose a filter

iirFilter.m

@@ -0,0 +1,60 @@
+function [signal_filtered, Z, P] = iirFilter(N, cutoffFreq, signal, samplingFreq, filterType)
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% function [signal_filtered, Z, P] = iirFilter(N, cutoffFreq, signal, samplingFreq, filterType)
+% ex.: [signal_filtered, Z, P] = iirFilter(6, [5 20], x, 200, 1)
+%
+% Task:
+%   To create and apply an IIR filter (Butterworth or Chebyshev)
+%   Supports low-pass or band-pass depending on the cutoffFreq input.
+%
+% Inputs:
+%   -N: order of the filter
+%   -cutoffFreq: scalar (for low-pass) or 2-element vector [low high] for bandpass
+%   -signal: input signal to be filtered
+%   -samplingFreq: sampling frequency in Hz
+%   -filterType: 1 = Butterworth, 2 = Chebyshev type I
+%
+% Outputs:
+%   -signal_filtered: filtered signal
+%   -Z: filter zeros
+%   -P: filter poles
+%
+% Author: Tikea TE
+% Date: 16/04/2025
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+% Design the filter
+if filterType == 1
+    if length(cutoffFreq) == 1
+        [b, a] = butter(N, cutoffFreq / (samplingFreq / 2), 'low');
+    elseif length(cutoffFreq) == 2
+        [b, a] = butter(N, cutoffFreq / (samplingFreq / 2), 'bandpass');
+    else
+        error('cutoffFreq must be scalar or 2-element vector');
+    end
+elseif filterType == 2
+    Rp = 10; % ripple for Chebyshev filter
+    if length(cutoffFreq) == 1
+        [b, a] = cheby1(N, Rp, cutoffFreq / (samplingFreq / 2), 'low');
+    elseif length(cutoffFreq) == 2
+        [b, a] = cheby1(N, Rp, cutoffFreq / (samplingFreq / 2), 'bandpass');
+    else
+        error('cutoffFreq must be scalar or 2-element vector');
+    end
+else
+    error('Filter type must be 1 (Butterworth) or 2 (Chebyshev)');
+end
+
+% Analyze zeros/poles
+[Z, P] = zeroPole(a, b, 1);
+
+% Show frequency response
+figure;
+freqz(b, a, N, samplingFreq);
+title('Frequency response');
+grid on;
+
+% Apply filter to signal
+signal_filtered = filter(b, a, signal);
+
+end