Calculating FT using matlab quad function

[lefti2003]

Hi All,
I am new to this forum and new to using the quad function. Some assistance would be most helpful. I appreciate all help in advance.

I have a .m file called OneExpDecay.m that has the following

syms t
x=exp(-2*t^2);
[RX,IX]=ft(x,-inf,inf);

then I have an ft.m that has the following

function [RX,IX]=ft(x,a,b)
syms t f
fr=@(t)x*cos(2*pi*f.*t);
RX=quad(fr,a,b);
fim=@(t)x*sin(2*pi*f.*t);
IX=-quad(fim,a,b);

When I run OneExpDecay.m I get the following errors that I do not understand how to resolve

?? Undefined function or method 'isfinite' for input arguments of type 'sym'.

Error in ==> quad at 81
if ~isfinite(y(1))

Error in ==> ft at 4
RX=quad(fr,a,b);

Error in ==> OneExpDecay at 3
[RX,IX]=ft(x,-inf,inf);





Thanks
Lefti

 

[KLoux]

The error that your receiving about functions being undefined for inputs of type sym means that you're trying to send a symbol into a function that is expecting a number (or numbers).

Here, my guess is that you need to use finite limits (inf and -inf won't cut it). Try replacing them with numbers.

Hope this helps.

-Kerry

 

[oswaler]

Hello Lefti,

It seems like the error is occurring because the quad function in your ft.m file is only designed to work with numerical inputs, not symbolic inputs. The isfinite function is used to check if a value is a finite number, and since your input is a symbolic expression, it is not recognized.

To resolve this issue, you may need to use a different function or approach to calculate the Fourier transform of a symbolic expression. You can try looking into the symbolic toolbox in Matlab or using other functions such as symsum or int to perform the integration.

I hope this helps. Good luck with your calculations!