MATLAB: Strange problem with sin.

sin problem

So i´m doing the following:
t = [0:0.5:5];
f = 2;
pha = pi/3;
x=sin(2 * pi * f * t + pha);
plot(t,x)
and the result on x will be
I´m pretty sure it´s my fault because i´m quite new, but i have already finished harder exercises and i just can´t find my mistake in this one. Any thoughts?

Best Answer

"Strange problem with sin."
So what is the problem? You did not tell us what you expect to get for the output values, or describe what the supposed "problem" is. We cannot guess what you imagine the output should be.
However what is clear is that sin has correctly calculated the sine values of the input values that you have given it, which have a step of 2*pi:
>> 2 * pi * f * t + pha
ans =
    1.0472    7.3304   13.6136   19.8968   26.1799   32.4631   38.7463   45.0295   51.3127   57.5959   63.8791
>> diff(2 * pi * f * t + pha)
ans =
    6.2832    6.2832    6.2832    6.2832    6.2832    6.2832    6.2832    6.2832    6.2832    6.2832
>> diff(2 * pi * f * t + pha)/2/pi
ans =
    1.00000   1.00000   1.00000   1.00000   1.00000   1.00000   1.00000   1.00000   1.00000   1.00000
All you have shown is that every 2*pi of its input sine's output repeats, which is exactly what we would expect (and is by definition of a circle).
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