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Re: Evaluating integral with varying upper limit?


It will be very helpful if you give your function f[x]

Regards
Dimitris

AES wrote:
> Given a function  f[x]  which happens to be rather messy and not
> analytically integrable, I want to evaluate the function
>
>    g[y_] := NIntegrate[f[x], {x, ymin, y} ]
>
> with ymin fixed and  ymin < y < Infinity.
>
> I suppose that FunctionInterpolate is the way to go here (???).
>
> But, are there tricks to tell FunctionInterpolate what I know in
> advance, namely that f[x] is everywhere positive, and decreases toward
> zero rapidly enough at large x that g[y] will approach a finite limiting
> value as y -> Infinity? (which value I'd like to have FI obtain with
> moderate accuracy -- meaning 3 or 4 significant digits, not 10 or 20)
> 
> Thanks . . .


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