Cos Magnitude changing for unknown reasons

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Robert 2016-9-28

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评论： Star Strider 2016-9-28

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

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Answer 1

Star Strider 2016-9-28

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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.

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Robert 2016-9-28

编辑：Robert 2016-9-28

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 2016-9-28

在 MATLAB Online 中打开

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