How to avoid NAN in a integration?

I don't know how to set the intevals of a integral to get the best precise result.

For example:This is the orginal definition of the formula.

y=integral(@(x) log2((f1(x))./(f2(x))), -inf, inf).

Note: f1(x)->0 and f2(x)->0 when x->-inf or inf, and the decreasing speeds are different.

If I use [-inf, inf] Matlab gives me NAN.

If I narrow down the inteval, Matlab gives a number. But if I increas the inteval a little bit, I get another number. So I am wondering how to deal this kind of integral calculation? How to make it as precise as possible without NAN?

Thanks a lot.

[Andrew Sykes]

It's not clear from your description of the problem that the integral will converge. For this integral to converge, you will need;

f1(x)./f2(x) -> 1 as x -> -inf or inf

(this condition alone won't suffice, but first check that this is indeed the case).

[smashing]

Hi Andrew, I tried a solution and it seems ok: y=integral(@(x) log2((f1(x))./(f2(x)+eps)+eps), -inf, inf).