Multiple errors with an integral

I am trying to find the energy of a signal in the frequency domain, but I am having trouble with the integral. I have had multiple errors which is why I did not choose one for the title. Some are: "Undefined function 'abs' for input arguments of type 'function_handle'", Error using integralCalc (...)set the 'ArrayValued' option to true..",etc.

This is the code:

clc
Fs=33280;
t = 0:1/Fs:(N/Fs)-(1/Fs);
N = 256;

x = 4*sin(1040*pi*t) + cos(3120*pi*t);

w = (-2*pi*Fs)/2:(2*pi*Fs)/N:(2*pi*Fs)/2-(2*pi*Fs)/N;

X =@(w) 1/N*fftshift(fft(x));

Px = integral((abs(X)).^2,-inf,inf);

disp(Px)

The error says: Undefined function 'abs' for input arguments of type 'function_handle'.

x is the signal in time, and X is the signal in the domain of frequency after Fourier.

Answer 1

[Steven Lord]

The abs function is not defined for function handles. You will need to create a new function handle that evaluates your original function handle and takes the abs of the values it returns:

absX = @(w) abs(X(w));

Now take the integral of absX instead of X.

[Reymi Chacon]

Thanks for the reply. I tried it but I get this error:

"Subscript indices must either be real positive integers or logicals."

The code is:

X = 1/N*fftshift(fft(x));

absX = @(w) abs(X(w));

Px = integral( absX,-inf,inf);

disp(Px)

T_T

[Walter Roberson]

You removed the @(w) from your definition of X. You still need a @()

X =@(x) 1/N*fftshift(fft(x));

It is not clear how your vector, w, of 256 (N) points, fits into all of this.

It looks to me as if w is intended to be your signal and that you are asked to calculate its energy. integral() is for calculating integrals of functions (or formulae) and you do not appear to have a function here. It appears to me that you should be doing a numeric integration such as by using trapz()

[Reymi Chacon]

Ah thank you. It seems trapz works without problems.

Answer 2

[nassima el ouarie]

please help me why the integration function is not working i don't know why ??

i want to compute this integral but this is what ti gives me matlab :

Error in integral (line 88)

Q = integralCalc(fun,a,b,opstruct);

Error in JENERALANDA (line 12)

JG1=integral(f,L1,L2);

this is the function i wrote to compute the integral :

function [JGL] = JENERALANDA()

syms L;

q=1.602176620*10^(-19);

Lw=(90*10^(-9));

w=(900*10^(-9));

N=50;

B=changalphaB();

Z=changalphaW();

L1=(0.24*10^(-6));

L2=(1.08*10^(-6));

f=@(L) ((2.3*10^(18)).*(1-exp(-B.*w-Z.*N.*Lw)));

JG1=integral(f,L1,L2);

JGL=-(q.*(JG1));

end

[Walter Roberson]

f=@(L) ((2.3*10^(18)).*(1-exp(-B.*w-Z.*N.*Lw)));

That does not use L, so no matter what the input it always returns the same output.