I am trying to fit measurement data.
(measured data is rather simple, as is the model)
However, I am struggling with the fit.
Two quantities were measured - lets call them x and y.
Plotting works and looks fine.
My model now gives me x and y as a a function of z and x(z). y is function of x (which is again a function of z). x is function of z and of simple (e.g. pol5) nature, but not invertible (i.e. I am not able to write y as a function of z )
So my graph looks like:
TGraph=TGraph(x(z) , y(x))
Is there an easy approach to fit my data and determine the coefficients of x(z)= pol5?
I am not sure if I have understood you correctly. You want to find the parameters of the function relating X to Z.
So X is not an independent variable, but a dependent one (on Z). Do you measure the variable X for different Z values ?
If this is the case, why you don’t fit directly X = f(Z) and forget about Y ?
Or if you measure also Y given X and you now the Y(X) relation, you can maybe do a combined fit of the X and Z data.
If I have misunderstood your use case, I concrete example might be useful
Can you elaborate more on the X and Y measurements ? You measure Y given X, or you measure Y and X independently ? Do you know z, when you measure X (or Y) ?
Again a descriptive example would be useful…