"I'm not sure I understand the pi/3, pi/4, etc. used in the x1-x4 equations below. Can anyone explain why this is included?"
A quick tutorial
figure;
t = 0 : 1/60 : 30;
plot(cos(t), 'k-')
hold on
The plot produced above is your base sinusoid. To change the frequency, multiply t by a value greater than one to increase the frequency or a value less than one to decrease the frequency.
plot(cos(t * 1.2), 'b-') %increase the freq.
To change the phase, add or subtract values from t. Adding values to t will shift the sinusoid leftward; subtractive values will shift if rightward. Try the block below.
figure
plot(cos(t), 'k-')
hold on
plot(cos(t + pi/6), 'b:') %shift leftward
You're working in radians so pi/6 is 30 degrees. If you shift it 360 degrees (2*pi in radians) the black and blue curves will overlap.
In your code (below), t is multiplied by 2*pi*.73 for whatever reason which changes the frequency of your sinusoid. The result is then added to pi/3 which shifts the phase. The reason the values are in fractions of pi is because you're working in radians.
x1 = 1*cos(2*pi*.73*t+pi/3);
"is a better more simple formula than what I have below"
That entirely depends on what you're doing. If you're just trying to create some sinusoids and their parameters don't matter, you could replace the 2*pi*.73 with whatever value that equals.
