Re: [Gnuplot-info] Factorial issue

[jody <jod...@gm...>]

Hi
Unless some gnuplot versions work with 32bit floats,
I'm surprised that it wouldn't work, because 100! = 9.33262154439442e+157
which is well inside the range of a (64bit) double...

Jody

>> > exponentiate at the end (if needed).

On Mon, Feb 8, 2010 at 5:04 PM, Philipp K. Janert <ja...@ie...> wrote:
> On Monday 08 February 2010 07:53:24 am Tim Wojtulewicz wrote:
>> On Mon, Feb 08, 2010 at 07:15:21AM -0800, Philipp K. Janert wrote:
>> > On Sunday 07 February 2010 11:07:07 am Tim Wojtulewicz wrote:
>> > > I'm working with a fairly complicated function, one part of which is
>> > > the division of two factorials.  I'm having an issue with though,
>> > > because gnuplot keeps returning NaN for what should be a simple
>> > > division.  It will return NaN for something as simple as 100!/99!,
>> > > which should just be 100. Is there a reason for this, or an easy way to
>> > > fix it?  Thanks.
>> >
>> > The intermediate results overflow, despite the fact that
>> > the final result is of meaningful size.
>> >
>> > Either work out the cancellations analytically, or work with
>> > logarithms of all quantities (Stirlings approximation!), and
>> > exponentiate at the end (if needed).
>>
>> So is this a version issue then?  The reply from Thomas seems like his
>> is working correctly.  I'm working with version 4.2.5 on OS X 10.6.
>> It's odd that his would work, and yet mine won't.
>
> If anything, this is a platform issue. Quite frankly,
> I was surprised that it worked for anybody. (It doesn't
> for me.)
>
> But this is besides the point: if you need factorials
> of large numbers (>10), then you need to find ways
> to tame overflow issues. Unless you are working in
> infinite precision integer arithmetic, which is not
> something that gnuplot does.
>
>>
>> Tim
>>
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