What is the better function for this curve?

[ValeryOchkov]

What is the better function for this curve?

The data in attach (Prime 5)!

Thanks!

[LucMeekes]

Try:

Success!
Luc

[LucMeekes]

And, of course, no solution without an animation:

Luc

[Fred_Kohlhepp]

Looks kind of like a hyperbola.  See attached in version 6.  (Solving for best parameters would require full Prime)

[DJF · Accepted solution]

Using zunzun.com it returns this as its best answer:

[ValeryOchkov]

Thanks!

Mathcad Prime <6 please!

[Werner_E]

You may create suitable values using "genfit"

[DJF]

my file in 5.0.  zunzun gave me the values, but you could do so with genfit or minerr as WE shows.  Hard part is finding the equation form.  zunzun is slow, but churns through 1000+ equation forms.

I followed up by converting to cylindrical coordinates, since vertical lines are often a challenge.  But I don't think it improved anything (red line below)

[Werner_E]

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@DJF wrote:

...

Hard part is finding the equation form. 

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Fully agreed on! I tried with Curve Expert Pro but I couldn't find anything that was anywhere near as good fitting.

I was not aware of zunzun - thanks for the hint. Have yet to learn how to use that page.

[DJF]

yes, it's confusing to use.

a.) select 2D pulldown - Function Finder

b.) click hyperlink to Function Finder

c,) pulldown - Text Data Editor.  Clear it out and Paste in your data (direct from excel works)

d.) pulldown - Equation Family Inclusion - select/deselect as needed.  (for your trial just pick one or else it's 1-2 hrs)

e.) Hit submit

f.) wait for results.  I've warned you ... it's slow.

g.) it returns the results in ranked order.  But then you have to click the link to that specific equation and rerun it, then you see a pdf with the actual values.

Tedious?  yes.  But free.  I've emailed the author and he's made changes for me.  So he's ahead of PTC in that regard.

Other options exist, like log plots, ranking criteria, etc.

[Werner_E]

Thanks for the detailed explanation - its indeed a bit confusing.

[ValeryOchkov]

I cannot open zunzun.com now.

Why?

May be only from Russia?

Check please!

[DJF]

It's down in the US also.  Hopefully will be back; lots of overloads on some systems in the last few days. 

[Werner_E]

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@ValeryOchkov wrote:

I cannot open zunzun.com now.

Why?

May be only from Russia?

Check please!

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The site is down or overloaded, no matter where you come from (you may try using a VPN, e.g. the free one in Opera).

In the meantime you may study the help

http://www.zunzunhelp.com/index.htm

or have a look at the discussion group here

https://groups.google.com/forum/#!forum/zunzun_dot_com

[DJF]

zunzun is back up.  

[DJF]

Much to my chagrin zunzun.com vanished from the net.  My understanding is the originator has some health issues.  Fortunately, I wasn't the only one who missed it.  It is now mirrored at the site findcurves.com