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# HELP! Fitting line into 5 points

## HELP! Fitting line into 5 points

(OP)
Hello everyone! :)

Is there anybody who could help me please?

I would like to fit a line into 5 fix points. I'm trying to do it with a function, but the problem is, that the x-axis has logarithmic scale.
Maybe I shoud use the loglinear version of the equation of the line, but it doesn't work...
Plase someone help me.

Thanks a lot!!!!
:)))

### RE: HELP! Fitting line into 5 points

As mentioned in the other thread, if you post the data or worksheet, it'll be easier to help you.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: HELP! Fitting line into 5 points

I did a quick Google search for "curve fitting with Mathcad" and found lots of sites that address your query, either directly or indirectly. Here are three examples. The first two are from the PTC website (BTW, Mathcad has functions for logarithmic and exponential regression.) and the other is from a university in the Middle East:

A more general, non-Mathcad resource you may find useful is "Curve Fitting for Programmable Calculator," by William M. Kolb. It's nearly 40 years old, but is still available through used book sellers. This book covers many different regression models. I would tell you more, but my copy is at the office. It appears that a PDF is available on scribd.com and a few other sites.

If you ever have more exotic curve fitting needs, I suggest CurveExpert: https://www.curveexpert.net/. I have the Professional version. I bought it about seven (?) years ago to try out different methods of approximating the Colebrook-White Equation (for hydraulics). Oh, and to address a curve fitting problem at work. (I wanted to try more than what the built-in capabilities in Excel and Mathcad were giving me.) I have also used CurveExpert to help me reverse engineer some complex nomographs.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

### RE: HELP! Fitting line into 5 points

It's a pretty straightforward thing; Excel can do the fitting with its trendline option and displaying its equation, which should take all of about 5 minutes.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: HELP! Fitting line into 5 points

(OP)
IRstuff.
I want to do it with Mathcad because I have more thing to do with the task. It's just a little part of it.
Okay, here it is:

In the graph you can see the elements of the matrix A. I put a circle around them. So what I want is to make the green line with a function. The green line must fit into the 5 points of the matrix A. Can you please help me?

### RE: HELP! Fitting line into 5 points

(OP)
Oh, what a pity... :( Thank you anyway :)

### RE: HELP! Fitting line into 5 points

Much ado about nothing; the segment is basically a straight line, and would be a perfect straight line, except that you seem to have a typo at the fourth data point, since you have 952 , but f(950)

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

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