created generate_trapezoid.m

src/generate_trapezoid.m

@@ -0,0 +1,55 @@
+function x = generate_trapezoid(amplitude, frequency, phase, fs, duration, duty)
+% GENERATE_TRAPEZOID: returns a matrix of sampled square wave
+
+% CONTRIBUTORS:
+% Daniel Doan: Author
+
+% 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 0.5 would have 2 trapezoids in first half of each cycle
+    % example of wave with duty of 0.5, where the peaks are amplitude/2: 
+    % 
+    %   ____ 
+    %  /    \
+    % /      \        ________________
+    %         \      /
+    %          \____/
+    % 
+
+
+
+% 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;
+        
+        % periodic ramp from 0 to 1
+        % progression through a cycle
+        st = mod(frequency * t - phase, 1);
+        slope = (amplitude/2) / (duty/8);
+        if(st < duty)
+            if(st < duty/8 || st > 7*duty/8)
+                x(i) = slope * st;
+            else
+                if(st < 5*duty/8)
+                    x(i) = amplitude/2 - slope * (st-(3*duty/8));
+                end
+                if(st < 3*duty/8)
+                    x(i) = amplitude/2;
+                end
+                if(st > 5*duty/8)
+                    x(i) = -amplitude/2;
+                end
+            end
+        end
+    end
+end