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Re: pade function in Octave?


From: Przemek Klosowski
Subject: Re: pade function in Octave?
Date: Fri, 1 Nov 2019 15:07:43 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

On 11/1/19 1:56 PM, vivek guajri wrote:
Hi Allen,

Thank you for your email. I have attached the excel file (includes x and y
values and pdf file of the fit and observed curve)
   x&y.xlsx 
<https://gcc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Foctave.1599824.n4.nabble.com%2Ffile%2Ft373519%2Fx%2526y.xlsx&amp;data=02%7C01%7Cprzemek.klosowski%40nist.gov%7C052da038cec047eabf0808d75ef4c953%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C1%7C637082277749877919&amp;sdata=DDhJqUN9oL9mHlip9pcIqw1gFKyNpz2ruqPxXlXYtUo%3D&amp;reserved=0>
   curvefitting.pdf
<https://gcc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Foctave.1599824.n4.nabble.com%2Ffile%2Ft373519%2Fcurvefitting.pdf&amp;data=02%7C01%7Cprzemek.klosowski%40nist.gov%7C052da038cec047eabf0808d75ef4c953%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C1%7C637082277749877919&amp;sdata=JWvH%2BDTY1CPTHBbIL7%2FplIxk7uwY4QlhhJ2MJg6jSWU%3D&amp;reserved=0>
  -

But the data in the .pdf are completely different from the data in your previous email---the former look like they may be fitted by a polynomial of a reasonably low degree, but the latter aren't. You of course can fit any data if you allow high order polynomials, but it's almost always a bad idea because such polynomials will behave crazily between and outside your data points.

Even the data from your .xslx spreadsheet look funny---there are discontinuities in the x values (between point 14 and 15, and between 19 and 20) that don't look real but suggest some sort of measurement error. They could be fit by a third-order polynomial but it looks wrong.

What is the data, what are the uncertainities of the data, and what is the physical model that you expect to predict the data? If you can answer these questions, then the fitted parameters of this model will have a physical meaning. Otherwise it'll be just more-less random numbers.




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