moved bandreject_filter() to src folder

src/bandreject_filter.m

@@ -0,0 +1,62 @@
+function output_y = bandreject_filter(Input, Fs, Low, High)
+    % A filter that lets through most frequencies unaltered
+    % but attentuates the frequencies in the specified range to
+    % very low levels
+    % (basically exliminates them)
+    % By Yalu Ouyang
+    
+
+    % Input: the input signal in the time domain
+    % Fs: the sampling frequency
+    % Low: the lower limit of the specified range
+    % High: the upper limit of the specified range
+    % Returns Output: the filtered signal in the time domain
+
+    len = length(Input);
+    
+    F = Fs * (-len/2 : (len/2 - 1)) / len ;
+    
+    % modified signal in the frequency domain
+    % using Fourier Transform
+    mod_freq = fftshift(fft(Input));
+    
+    len_f = length(mod_freq);
+    
+    % use this array to record the frequencies
+    % that should pass through
+    % 0 indicates reject
+    % 1 indicates pass
+    multiplier =  zeros([1,len_f]); 
+    
+    for index = 1 : len_f
+
+        % within range of band reject
+        % so elminate these frequencies
+        if ((Low < abs(F(index))) && (abs(F(index)) < High))
+            multiplier(index) = 0;
+        
+        % outside of specified range
+        % so shoudln't be altered
+        else
+            multiplier(index) = 1;
+        end
+    end
+    
+    % filtered signal in the frequency domain
+    filtered_mod_freq = fftshift(mod_freq .* multiplier);
+    
+    % convert signal back to the time domain
+    Output = real(ifft(filtered_mod_freq));
+    
+end
+
+% This function is useful for eliminating
+% unwanted signals that have frequencies close to the 
+% median frequency of the original signal
+% (consider overall frequencies as one part, 
+% this elminates the middle portion)
+
+% Fourier transform is applied in this function
+% to make it easier to eliminate specified 
+% frequencies of the signal
+% (easier to do so in the frequency domain)