# [Ifeffit] number of independent points

Matt Newville newville at cars.uchicago.edu
Mon Oct 10 10:30:28 CDT 2011

```Hi George.

It should be 2*(Delta k)*(Delta R), without the +2, but as a floating point
number.   That is, it is deliberately conservative.  I believe the subtle
difference you see (that is why the value is 27.06 instead of 27.5) must be
due to rounding of the R values on to a discrete grid.

-Matt
On Oct 10, 2011 9:35 AM, "George Sterbinsky" <
GeorgeSterbinsky at u.northwestern.edu> wrote:

> Hello,
>
> Since I haven't received a response to my previous question, I just wanted
> to make sure I asked it clearly. To elaborate, I am attaching a log from
> Athena. The log file lists:
>
>  "Independent points          =      27.057617188"
>
> If I attempt to reproduce this result using the equation in the feffit
> document, I find
>
> Nidp = { [2*(kmax - kmin)*(Rmax-Rmin) / pi] + 2} = { [2*(14 - 0.5)*(4.2 -
> 1.0) / pi] + 2} = 29.50197417,
>
> where I have used the k-range and R-range in the log file as kmax, kmin,
> Rmax, and Rmin.
>
> Can someone explain to me why may calculation does not reproduce the number
> given for "independent points" in the log fie?
>
> Thank you,
> George
>
> On Fri, Oct 7, 2011 at 1:04 PM, George Sterbinsky <
> GeorgeSterbinsky at u.northwestern.edu> wrote:
>
>> Hello,
>>
>> I am wondering what values Artemis/feffit use for kmax and kmin when
>> calculating the number of independent points (Nidp) for a fit done in
>> R-space, where according the feffit document, Nidp = { [2*(kmax -
>> kmin)*(Rmax-Rmin) / pi] + 2}, and kmax and kmin define the fitting range. I
>> have tried using the Fourier transform range for kmax and kmin, but this
>> does not give agreement with the value of Nidp reported by Artermis.
>>
>> Thank you,
>> George
>>
>
>
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