# matlab - finding amplitude, frequency & periodic time of given sine wave

Discussion in 'Programmer's Corner' started by wick54, Dec 4, 2008.

1. ### wick54 Thread Starter New Member

Dec 4, 2008
3
0
hi every one,
i'm trying to find amplitude, frequency & periodic time of given sine wave using matlab
actually the equation is y = 2sin3x and x is -4pi<x<4pi
so what commands shoud use in matlab to find those variables

in addition, i need to draw the fequency domain plot for the above given plot using matlab
thank you

2. ### blazedaces Active Member

Jul 24, 2008
130
0
Seriously? A teacher actually assigned this to you? These numbers are obvious by observation based on a simple equation: y = A*sin(2*pi*f*x+phase). Honestly, what in the world is the point of learning how to obtain it through matlab?

Sorry, I just feel it seems like a stupid assignment. But that doesn't really help you does it. Anyway, as you can see I've shown you how you can easily obtain these constants via observation in real life. That should explain to you certain ways you can go about it.

So... do you have any idea what a frequency domain plot even is? What issues are you having with this problem? Do you know how to do these things normally and are having trouble with matlab? What have you done so far on your own that we can help you with?

-blazed

3. ### wick54 Thread Starter New Member

Dec 4, 2008
3
0
thanks bro, what about the 2nd part??? do you guys know abt to draw the fequency domain plot for the above given plot using matlab??
than you

4. ### blazedaces Active Member

Jul 24, 2008
130
0
Sure.

Now, do you know what a frequency domain plot actually is and how to obtain it without matlab? As in by hand? If you do, matlab makes it incredibly easy...

-blazed

5. ### wick54 Thread Starter New Member

Dec 4, 2008
3
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actually i have no idea how to make to by hand, can you please tell me how can i use matlab to plot it???

6. ### blazedaces Active Member

Jul 24, 2008
130
0
I don't understand, what kind of class tells you to do something you've never even heard of by hand... in a computer?

The concept of the frequency domain. Do you know where that comes from? Do you know what it means? Even in very simple terms?

Do you know what is the fourier transform?

-blazed

7. ### Aesh New Member

Mar 27, 2009
2
0

hi..i ws searching on how do v study the waveforms in frequency-domain graph. i came accross this post..n really wnt to know how a frequency-domain plot is drawn by hand?
Thnx

8. ### dig1 Member

Jul 31, 2008
18
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frequency domain plot is done with two things:

like just a regular graph, frequency graph has two variables.... W - omega and the magnitude of the transfer function or the function expressed in the s-domain or frequency domain. usually these are the fourier coefficents....just graph these two variables on a graph like you would a regular equation