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Using NIntegrate[] within FindRoot[] ??

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  • Subject: [mg2306] Using NIntegrate[] within FindRoot[] ??
  • From: a_kowald at (Axel Kowald)
  • Date: Mon, 23 Oct 1995 12:43:19 -0400
  • Organization: Kristallographic Institute FU Berlin

Hello everybody

I like to use NIntegrate with FindRoot as in the following trivial example:

            FindRoot[NIntegrate[r x,{x,0,3}] == 9, {r,1}]

That means I want to find the value of "r" for which the integral is equal to 9.
However, I get the error message:

                Integrand 1.5 r is not numerical ...

What am I doing wrong and how am I doing it right ???

Many thanks in advance

		Axel Kowald

P.S. I know that the example is more than trivial, I just used it for 
     illustrative purposes. I also know that I can write a function which 
     iterates several values for r, but if I could use FindRoot its definitely
     the most elegant way.

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