Cos Magnitude changing for unknown reasons

This is probably not mat labs fault but i don't understand why my magnitude is changing

If i plot

.5*cos(x)

no surprise my min and max magnitude of the function is -.5 and plus .5

if i plot

.5*cos(2*pi*60*x)

My min max magnitude is changing from -.4 to .5 Why am i loosing .1 on the bottom just by changing the frequency

Answer 1

[Star Strider]

I don’t know what ‘x’ is, but what you are probably seeing is the phenomenon known as ‘aliasing’, where your sampling frequency is lower than the frequency of your cosine function.

[Robert]

X can be anything

Call it 0 to 2*pi if you want I have had the problem on any interval

Im not sampling anything although i know what ur talking about from DSP

This is just sampling referring to any old plot of cos(x)

You can even do this in wolfram

Plot .5cos(x) and i get -.5 and .5 then plot .5cos(2*pi*60*x) and all of a sudden my plot is -.4 to .5 No clue why

[Star Strider]

Not the interval, the sampling frequency.

Example:

x = linspace(0, 1, 1200);
y = .5*cos(2*pi*60*x);

min_max = [min(y), max(y)]

figure(1)
plot(x, y)
grid

min_max =
        -0.499998283668634                       0.5

This is about as close as you can reasonably get. The inaccuracies are likely those inherent to any floating-point calculations.