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MathGroup Archive 2001

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Re: Re: slow integration


After reading your message, I'm also sure I don't understand your problem.
You say "the integral is evaluated without delay":

In[1]:=
> Timing[InputForm[Integrate[Erf[400 (z/x-.002)],{x,0,.03}]]]
> Out[1]=
> {0.45 Second,Integrate[Erf[400*(-0.002 + z/x)], {x, 0, 0.03}]}

But, is this an evaluation or just writing back what you gave as input?

Tomas Garza
Mexico City

----- Original Message -----
From: "Joshua A. Solomon" <J.A.Solomon at city.ac.uk>
To: mathgroup at smc.vnet.net
Subject: [mg29958] Re: slow integration


> I'm not sure that you really understand the problem. (I *am* sure that I
do
> not understand the problem.) Note that, without the Gaussian factor in the
> integrand, the integral is evaluated without delay:
>
> In[1]:=
> Timing[InputForm[Integrate[Erf[400 (z/x-.002)],{x,0,.03}]]]
> Out[1]=
> {0.45 Second,Integrate[Erf[400*(-0.002 + z/x)], {x, 0, 0.03}]}
>
>
> On 19/7/01 9:26 am, in article 9j65j1$2gh$1 at smc.vnet.net, "Tomas Garza"
> <tgarza01 at prodigy.net.mx> wrote:
>
> > You will not get any result. I guess the problem is that Erf[z] doesn't
have
> > a closed form and it remains expressed as a definite integral.
> >
> > Tomas Garza
> > Mexico City
> >
> >
> > ----- Original Message -----
> > From: "Joshua A. Solomon" <J.A.Solomon at city.ac.uk>
To: mathgroup at smc.vnet.net
> To: mathgroup at smc.vnet.net
> > Subject: [mg29958]  slow integration
> >
> >
> >> In[1]:=
> >> $Version
> >> Out[1]=
> >> 4.1 for Power Macintosh (November 2, 2000)
> >>
> >> Does anyone out there understand why, after two hours, the following
still
> >> hasn't produced any output?
> >>
> >> In[2]:=
> >> Integrate[E^(-100000 (.03-x)^2)Erf[400 (z/x-.002)],{x,0,.03}]
> >>
> >> js
> >> --
> >> Joshua A. Solomon
> >> Department of Optometry and Visual Science
> >> City University
> >> London EC1V 0HB
> >> Voice: (44) 20 7040 0192
> >> Secretary/Fax: (44) 20 7040 0182
> >> J.A.Solomon at city.ac.uk
> >> http://www.staff.city.ac.uk/~solomon
> >>
> >>
> >
> >
>
>



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