Re: equation to fit data

From: Art M (Xarthurruhtra_at_netscape.netX)
Date: 02/25/05 

Date: Fri, 25 Feb 2005 13:12:10 -0500

Thanks to everyone for your help so far.

The data are from a cycling website. X is tire pressure (psi) and y is a
factor to get the resulting coefficient of rolling resistance where 120 psi
(a fairly standard inflation pressure) is baseline. I assume that from 0 to
some minpsi you get a near horizontal line where the rim is riding on the
rubber and above that you get the curve that the points given indicate. The
data shows that increasing pressure has proportionally less of an
improvement in CRR the higher you go.

The points I gave came from a calculator on the website so I assume they
perfectly fit some relatively simple equation that was made to approximate
the test data. I understand that you can always come up with some polynomial
that approximates your data. I'll have to read up on least-squared
regression. Is there a similar method to come up with an equation that uses
a function like LOG?

I suppose I could send an email to the website creator, but this is helping
to recover some of my very rusty math skills.

Art

"Michael Jørgensen" <ccc59035@vip.cybercity.dk> wrote in message
news:421f0d46$0$295$edfadb0f@dread12.news.tele.dk...
> "Art M" <Xarthurruhtra@netscape.netX> wrote in message
> news:EWzTd.10922$7z6.5991@lakeread04...
>> I don't suppose anyone could find the/an equation that created this data
> (or
>> tell me how to derive it)?
>>
>> x, y
>> 90 , 1.1655
>> 100, 1.0957
>> 110, 1.0414
>> 120, 1
>> 130, 0.9696
>> 140, 0.9483
>> 150, 0.9347
>
> You really need to know some more about your data. What is the range of x
> and y? Is x always positive, or may x become negative too? What about y,
> is
> it always decreasing? Is it always positive? If you know where the data
> comes from, you should be able to answer these questions.
>
> Once you have this information, this will help to narrow done the list of
> potential functional relationships.
>
> BTW, what is the accuracy of your data? It looks like the y values are
> measurements. Are you able to repeat these measurements? This will help
> estimate the accuracy of the data.
>
> -Michael.
>
>

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