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From: Regina on 18 Feb 2010 05:15
Hi there,
i got a problem: how can i evaluate the following integral:
define:
i[Q_] := Integrate[(Exp[-a/(4 x) - 4 x]), {x, \[Infinity], Q}]
now i want to compute:
NIntegrate[1/i[Q], {Q, 0, 1}]

what am i doing wrong? how can i integrate that function?

From: dh on 19 Feb 2010 03:35


you may do it like:



fun[Q_?NumericQ]:= NIntegrate[(Exp[-1/(4 x) - 4 x]), {x, Q, \[Infinity]}]

On 18.02.2010 11:15, Regina wrote:

> i got a problem: how can i evaluate the following integral:

> define:

> i[Q_] := Integrate[(Exp[-a/(4 x) - 4 x]), {x, \[Infinity], Q}]

> now i want to compute:

E-Mail:<mailto:dh(a)metrohm.com>

Internet:<http://www.metrohm.com>



From: Kevin J. McCann on 19 Feb 2010 03:35
You did not specify what a is. In NIntegrate it has to be a numerical
value. Also, the "_?NumberQ" construct prevents NIntegrate from trying
any symbolic tricks and giving errors.

Clear[i, Q]
a = 1.0;
i[Q_?NumberQ] := NIntegrate[Exp[-(a/(4 x)) - 4 x], {x, \[Infinity], Q}]

NIntegrate[1/i[Q], {Q, 0, 1}]

I get -71.477 for this.

Kevin

Regina wrote:
> Hi there,
> i got a problem: how can i evaluate the following integral:
> define:
> i[Q_] := Integrate[(Exp[-a/(4 x) - 4 x]), {x, \[Infinity], Q}]
> now i want to compute:
> NIntegrate[1/i[Q], {Q, 0, 1}]
>
> what am i doing wrong? how can i integrate that function?
>

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