- To: mathgroup at smc.vnet.net
- Subject: [mg5933] Re: [mg5865] Integration
- From: Daniel Lichtblau <danl>
- Date: Tue, 4 Feb 1997 00:04:21 -0500
- Organization: Wolfram Research, Inc.
- Sender: owner-wri-mathgroup at wolfram.com
Mark Dowell wrote:
> I have a question involving the definite INTEGRATE function.
> With integration you give Mathematica; the function of x, and the values of
> x between which you want it integrated. My problem is that I KNOW the area
> I want (and know that I am using the origin as xmin) but I need Mathematica
> to calculate xmax for me.
> In words my equation is:
> CHLstep = the integral (with respect to x) of the function CHLfunc(between 0
> and certain value of x)
> Where what I need is what value of x will make that statement true. (CHLstep
> is a fraction.)
> Mark Dowell Ispra, I-21020, (VA)
> Marine Environment Unit TP 272 Italy.
> Space Applications Institute E-mail: mark.dowell at jrc.it
> Joint Research Centre Talk: dowell at biscay.jrc.it
> Ispra Site Phone: +39-332-789873
> Commission of the European Communities Fax: +39-332-789034
If the indefinite integral can be computed, you can do
f[x] = Integrate[g[x], x]
Assuming no bad discontinuities, that is, definite integral is equal to
evaluated indefinite integral, you then simply do
If you cannot get the indefinite integral, you might try approaching
this problem numerically. Using NIntegrate and various upper bounds,
subdivide the region in which you place a trial xmax until it gives an
integral sufficiently close to the area.
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