Cos Magnitude changing for unknown reasons

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Robert
Robert 2016-9-28
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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回答（1 个）

Star Strider
Star Strider 2016-9-28
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.
  2 个评论
Robert
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
Star Strider 2016-9-28
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.

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