Fit function to plotted graph (that resembles the shape of a haft circle)

Forum|Forum|3 years ago
February 20, 2023
17 replies
4918 views

Hi

I have plotted the results from two vectors. The graph resembles the shape of a half circle and I would like to find a function that fits the data so intersection points can be determined for other functions.

I have tried many different curve-fitting tools but can't find a proper one that works.

I'm thankful for any help!

1_Fit-function-to-curve.zip

Mathcad Usage

Best answer by Werner_E

I get slightly different values using CurveExpert Pro

And I get similar values in Prime using genfit() (though genfit is VERY sensible wrt the guess values).

BTW, as we can see far to the right of the Prime sheet how the data is actually calculated it should not surprise that a sinusoidal fit is suggested by CurveExpert 😉

F

Fred_Kohlhepp

23-Emerald I

If I digitize the data, then rotate it so X is a function of Y, and send it to CurveExpert,, I get

Which has the form

Prime 4 attached

1_vectors-fit.zip

W

Werner_E

Answer

25-Diamond I

I get slightly different values using CurveExpert Pro

And I get similar values in Prime using genfit() (though genfit is VERY sensible wrt the guess values).

BTW, as we can see far to the right of the Prime sheet how the data is actually calculated it should not surprise that a sinusoidal fit is suggested by CurveExpert 😉

K

ksk_10594232

Author

12-Amethyst

Wow! Thanks for the good explanation!

F

Fred_Kohlhepp

23-Emerald I

It is possible to define functions rather than vectors for your plots:

I've done it in the attached Prime 8 Express sheet.

Attempts to solve for the intersection (in Express) have failed; maybe someone with a solve block capability?

Note that it's possible to create functions only using the parameter "y", which would result in a single intersection point. I introduced a second variable (l_k) hoping to be able to trace the intersection point as a function of that variable.