Re: slow integration

• To: mathgroup at smc.vnet.net
• Subject: [mg29958] Re: slow integration
• From: "Joshua A. Solomon" <J.A.Solomon at city.ac.uk>
• Date: Fri, 20 Jul 2001 03:28:24 -0400 (EDT)
• References: <200107180608.CAA18960@smc.vnet.net> <9j65j1\$2gh\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```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
> 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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