Unexpected result for sin()
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Dear all;
I think I'm getting crazy or something. Fact is that Matlab is giving me some strange results for a simple sin function.
If I try and run the following:
f=30;
x=0:0.01:1;
y=0.7*sin(2*pi*f*x);
plot(x,y)
I get a simple wave plot.
Now, if I change f to 50, then I get this strange plot:
How is that possible?
Thank you!
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Answers (4)
Wayne King
on 1 Dec 2012
Edited: Wayne King
on 1 Dec 2012
Because you are evaluating sin() at multiples of pi
2*pi*k/2
Each one of your steps in x is a multiple of 1/100, then you are multiplying that by 50 when f=50 so you are evaluating sin() at multiples of 2*pi*k/2 and they will all be essentially zero. Look at the y-axis of your plot. Those numbers are all essentially zero.
Actually even your 30-Hz sine does not look that good because you are sampling your x-vector too coarsely, compare for example
x = 0:0.01:1;
xprime = 0:0.001:1;
y = sin(2*pi*30*x);
yprime = sin(2*pi*30*xprime);
subplot(211)
plot(x,y)
subplot(212)
plot(xprime,yprime)
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Azzi Abdelmalek
on 1 Dec 2012
Edited: Azzi Abdelmalek
on 1 Dec 2012
f=50;
np=5 % number of period
t1=np/f % final time
ns=20 % number of sample per period
ts=1/(ns*f) % sample time
x=0:ts:t1;
y=0.7*sin(2*pi*f*x);
plot(x,y)
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