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MathGroup Archive 2000

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Re: Integrate with If

  • To: mathgroup at smc.vnet.net
  • Subject: [mg22275] Re: Integrate with If
  • From: "Johan Berglind,5879" <johanbe at chl.chalmers.se>
  • Date: Mon, 21 Feb 2000 20:00:45 -0500 (EST)
  • Organization: Chalmers University of Technology
  • References: <88g62h$4mq@smc.vnet.net> <88jtvv$9n3@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

> 
> The "If" construct is an impropper argument for Integrate, see the
> online-help:
> (...)
> Integrate can evaluate integrals of rational functions. It can also
> evaluate integrals that involve exponential, logarithmic, trigonometric
> and inverse trigonometric functions, so long as the result comes out in
> terms of the same set of functions.
> (...)
> 

Thank you, Harald.

As you and many others have pointed out, If is not suited for use in
Integrate. 
It does, however work most of the time; 
	Integrate[If[Sin[t]>0,1,0], {t,-Pi/2,Pi/2}]
gives the correct answer. (The critical point seems to be -Pi)
And it seems to be fairly efficient. (Try using it in FourierSeries.)

My point is that either should If work in Integrate all of the time (and
I believe that is the ambition of Wolfram) or Mathematica should at
least produce a warning.

Johan.


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