Fitting Data to a Prescribed Equation

2017 10 22
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更新时间：2017 10 23
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I have an equation of the following form
Nu=A*(0.75+0.013*ALFA)*(RE)^(m)*0.711^(1/3)
Where ALFA and RE are a set of prescribed values
ALFA=0 5 10 15 20 25 Re= 200000 300000 400000 500000
Nu is a set of values obtained from simulations
I know that my equation should look like the one previously shown, I would like to solve for the coefficients A and m so my prescribed values validate the equation
Any help please?

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dpb
dpb 2017-10-22
How do you expect to use the resulting correlation; as function which variables?
You use nonliner fitting; convert the measured data to values of the correlation at the points for which you have the values at those points for which you have the data.
You may have issues of correlation/estimation depending on the locations of those points; you've not given that much info; try it and find out what happens...
As for which tools to use for the fitting, depends on which toolboxes you have; there are routines in either the Curve Fitting or the Statistics TBs or you can use the fminsearch routine in base product having neither of the above....
Abdallah Samad
Abdallah Samad 2017-10-22
Hey thank you for your answer. I do understand the procedure you outlined but I have no idea how to write in MATLAB language.
THe figure shows the results of simulations I got. and on top of each table I put the associated correlations to which I would like to get my coefficient A and B.
Do the entries in the table correspond to values of Nu?
dpb
dpb 2017-10-23
编辑：dpb 2017-10-23
But you've still not told us which toolsets you have available to use...also, attach data as text so somebody could do something with it rather than just look at it.
dpb
dpb 2017-10-23
Also, please clarify the equation -- is the power term at the end
RE^[m*Pr^1/3]
or
(RE^m)*Pr^1/3
or yet some other grouping? My initial fitting with the first isn't promising at all...
Abdallah Samad
Abdallah Samad 2017-10-23
Hi please attached the vales within the PDF As for the power term, its actually the second one you wrote Thank you very much !

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回答（1 个）

Nicolas Schmit
Nicolas Schmit 2017-10-23
编辑：Nicolas Schmit 2017-10-23

0 个投票

If I am correct, what you are trying to do is to fit a nonlinear model to a data set. The MATLAB command to do that is fitnlm. Look here for an introduction to nonlinear regression.

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