Re: NIntegrate of a Decaying Exponential

*To*: mathgroup at smc.vnet.net*Subject*: [mg15192] Re: NIntegrate of a Decaying Exponential*From*: "W. K. Bertram" <wkb at ansto.gov.au>*Date*: Fri, 18 Dec 1998 02:11:08 -0500*Organization*: Australian Nuclear Science and Technology Organisation*References*: <75a179$rv3@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

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