How to find equation when i have points?

Specific Domains Numerics
1

I have points and need to get equation of these points. I try to use wolfram and another online services and all result is bad.

2

Plots:

image
image754×577 7.65 KB

data: Plots - Google Drive

3

You could use Polynomials.jl to fit a polynomial in the y-axis variable.

For a 4th-order polynomial, this gives:

Polynomials_4th_order_fit
Polynomials_4th_order_fit885×579 38 KB

2 Likes
4

Thank you very much!
Can you share code? I don’t know how to convert data from .mat to .jl. I can convert to numpy array and then to .jl, but it long

5

Sorry, I did this in the REPL and the code is a mess to cut and paste.

To read the Matlab files, I have used the MAT.jl package.

6

What am i doing wrong?

f4 = fit(I0_data, U0_data, 4)
-725636.891507482 - 1.9486539668049992e6∙x - 1.9622241946502575e6∙x^2 - 878106.3537953914∙x^3 - 147347.79216010476∙x^4

function equat(x)
    -725636.891507482 .- 1.9486539668049992e6*x .- 1.9622241946502575e6*x.^2 - 878106.3537953914*x.^3 .- 147347.79216010476*x.^4
end

ytest = equat(I0_data);

image
image600×600 21 KB

7

I think you need to switch between I0_data and U0_data as the arguments usally go x = p(y) and you want to fit polynomial over y input value with x output value.

8

It helped, thank you!