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Re: IDL is not accurate enough! [message #62511 is a reply to message #62188]

Thu, 11 September 2008 07:10

noahh.schwartz
Messages: 10
Registered: February 2008

Junior Member

On 28 août, 18:42, FÖLDY Lajos <fo...@rmki.kfki.hu> wrote:
> On Thu, 28 Aug 2008, noahh.schwa...@gmail.com wrote:
>> Hi,
>
>> I've been having problems with IDL accuracy. I'm trying to perform
>> calculations using the gamma function. The problem is that it grows
>> VERY fast! Performing this calculation in double (namely gamma(x)/
>> gamma(y) with x and y big) yields the result: NaN...
>> Would it be possible to use a program like 'Mathematica' (or any
>> other) and to plug it in my ILD program? Some kind of CALL_EXTERNAL
>> that is to say. If it is possible, how can I do it and what is the
>> best program to use?
>
>> Thanks,
>> Noah
>
> gamma(x)/gamma(y) => exp(lngamma(x)-lngamma(y))
>
> regards,
> lajos

lngamma works fine for my propose! Would you know if an equivalent
function exists for the beselk function? Something like lnbeselk?
beselk(x) for x>709 doesn't seen to work.
If not, I guess that I'll have to wait for the DLMs that add arbitrary
precision floating point...

cheers,
Noah

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[Message index]

		Re: IDL is not accurate enough! By: Kenneth P. Bowman on Thu, 28 August 2008 13:50
		Re: IDL is not accurate enough! By: Foldy Lajos on Thu, 28 August 2008 09:42
		Re: IDL is not accurate enough! By: David Fanning on Thu, 28 August 2008 09:35
		Re: IDL is not accurate enough! By: noahh.schwartz on Thu, 11 September 2008 07:10
		Re: IDL is not accurate enough! By: rtk on Thu, 04 September 2008 11:46
		Re: IDL is not accurate enough! By: Haje Korth on Mon, 08 September 2008 06:45

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