additional comments for :

generate_sine,
generate_square,
generate_triangle,
from Benjamin Liou

src/generate_square.m

@@ -1,19 +1,40 @@
 function x = generate_square(amplitude, frequency, phase, fs, duration, duty)
-%GENERATE_SINE:Arthur Lu returns a matrix of sampled sine wave, where the
-%phase shift is in number of periods
-    x = zeros(1, fs * duration);
-    A = amplitude;
-    f = frequency;
-    p = phase;
-    n = fs * duration;
-    dt = 1 / fs;
+% GENERATE_SQUARE: returns a matrix of sampled square wave
+
+% CONTRIBUTORS:
+% Arthur Lu: Original author
+% Benjamin Liou: refactoring and annotations
+
+% DOCUMENTATION:
+% phase shift is in number of periods
+% fs is the sampling frequency: how many sample points per second
+% duration is time in seconds
+% duty cycle should be a number between 0 and 1.
+    % duty of 0 or less would return -amplitude for all sample points
+    % duty of 0.25 would return +amplitude for first quarter of each cycle
+        % then return -amplitude for the remaining three-fourths
+    % duty of 1 would return all +amplitude
+
+
+% initialize local variables from input arguments
+    n = fs * duration; % number of samples (length of matrix)
+    dt = 1 / fs; % sampling period: time between two sample points
+    
+    % initialize a one dimensional zero matrix to be populated
+    x = zeros(1, n);
+    
+    % populate the matrix
     for i = 1:n
-        t = i * dt;
-        st = mod(f * t - p, 1);
+        t = i * dt; % time at the i'th sample
+        
+        % periodic ramp from 0 to 1
+        % progression through a cycle
+        st = mod(frequency * t - phase, 1);
+        
         if(st < duty)
-            x(i) = A;
+            x(i) = amplitude;
         else
-            x(i) = -A;
+            x(i) = -amplitude;
         end
     end
 end