comp.lang.idl-pvwave archive: archive » value of a function at y(0) given the definite integral

Home » Public Forums » archive » value of a function at y(0) given the definite integral

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: value of a function at y(0) given the definite integral [message #27550 is a reply to message #27378]

Fri, 26 October 2001 13:28

John-David T. Smith is currently offline

John-David T. Smith
Messages: 384
Registered: January 2000

Senior Member

aqueous wrote:
>
> Say I know the shape of a function y(x). Say it's x^2.
> Say I know the integral from a to b of this function. Say it's 1.0.
>
> What I want to do is find out the value of the function at y(0) given
> the info above, mainly
>
> y(x) = x^2
> integral_ab(y(x)) = 1.0
> What's the value of y(lowerLimit)?

> Does this make sense??

No, I suppose not. If you have the function in hand, then:

y(x=0)=y(0)=0^2=0

Presumably this result was obvious to you too, and you mean you have an
integral over some limits and want to use this information to find the
value at x=0, without knowing the function itself? This is of course
impossible.

Perhaps what you *really* mean is you have some function like:

y=Ax^2

where you want to determine an overall normalization constant "A" from a
known integral over a fixed range of the given functional form. This is
a much more sensible problem, and quite common in practice. It can be
approached numerically (for which IDL can offer some help), or
analytically (for which IDL is useless). In both cases, the simple
relation:

integral(Ay(x) dx)=A integral(y(x) dx)

will guide the way.

JD

Report message to a moderator

[Message index]

		value of a function at y(0) given the definite integral By: aqueous0123 on Mon, 22 October 2001 13:41
		Re: value of a function at y(0) given the definite integral By: a on Fri, 26 October 2001 15:24
		Re: value of a function at y(0) given the definite integral By: John-David T. Smith on Fri, 26 October 2001 13:28
		Re: value of a function at y(0) given the definite integral By: aqueous0123 on Fri, 26 October 2001 12:55

Previous Topic:	PLOT question
Next Topic:	Re: Other IDL / Mac advantages

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sat Oct 11 09:46:18 PDT 2025

Total time taken to generate the page: 0.56119 seconds