Nope. Not possible. There are no simple "functions" there.
These are splines. So they are composed of MANY tiny polynomial segments. That is what a spline is.
Honestly, look at those plots. Do you really think there would be some simple function that yields those curves? Not going to happen.
As for using a polynomial, do not bother. Any polynomial that fits those points will be pure crapola between the points.
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