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# find the mean, energy and power of cosine function

Asked by Passband Modulation on 21 Sep 2012
Latest activity Commented on by Walter Roberson on 18 Dec 2013

i am just a matlab beginner.

x[n]=2cos(0.2*pi*n) with a length of N =100 , that is, ,0<N<99 plotted

``` clear all
n=[0:99];
x=2*cos(0.2*pi*n);
stem(n,x);
legend('x[n]');
title('Sequence of 2*cos(0.2*pi*n)');
xlabel('n');
ylabel('x[n]');
axis([0 99 -2 2]);```

how to use MATLAB to compute the mean, and energy and power of x[n]given mean=x, energy=Ex and power=Px.

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Answer by Wayne King on 21 Sep 2012
Edited by Wayne King on 21 Sep 2012

You can just do:

```      mean(x)
Ex = norm(x,2)^2  % the energy
Px = 1/numel(x)*norm(x,2)^2 % power```

If you don't want to use norm(), you just use sum()

```      Ex = sum(abs(x).^2)
Px = 1/numel(x)*sum(abs(x).^2)```

Note that the RMS of the signal is

`      sqrt(Px)`

The Signal Processing Toolbox implements this as rms()

Passband Modulation on 21 Sep 2012

thank you very much, it works well!!

Walter Roberson on 18 Dec 2013

pinak parida commented,

```power ,energy of a signal how norm works to be check?
```