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Re: NIntegrate of a Decaying Exponential


Wretch wrote:

> Greetings -- I'm trying to get Mathematica to do an integral that
> appears regularly in plasma physics problems.  It appears to give the
> right answer, but it's always accompanied with an annoying error
> message whose roots are a bit vague.  Here is the function to be
> integrated:
>
> f = -2 v Exp[-v^2]  over the v-interval  (-1,2)
>
> The answer should be about  -.34956 (according to an IMSL subroutine)
>
> Here's the mathematica input and output:
>
> In[1]:=NIntegrate[-2 v Exp[-v^2],{v,-1,2}] Out[1]:=Out[99]=-0.349564

I don't know what version of mathematica you are using or on what
platform, but
version 3.0 under win95 on a PC, gives no message when using "Intergate"
or "NIntegrate".

"The answer should be about  -.34956 (according to an IMSL subroutine)"


You don't need an IMSL routine to tell you that! The integral is such a
simple
one, after all the integral of -2vExp-v^2] is just Exp[-v^2]. Put in the
limits
and you'll get  1/e^4-1/e.

Cheers,
        Bill



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