Curve fitting on Data with three variable X,Y,Z

[deleted_user]

I have data with 3 variables X,Y,Z and i want to fit a model like ...
Y= a(x) + b(z)+c,
X and Z may have some powers (n) also.How to do it? Please guide

[Dale]

Your problem specification is incomplete. Let me respond by first asking a few questions.

Why do you think you should use powers of X and Z? Are those powers prespecified? Are X and Z nonnegative? If the powers are not prespecified integer values, then you could run into problems if the algorithm which is used to fit the model tries to raise a negative value to a noninteger power.

Do you want to consider polynomial functions of X and Z? The model below is representative of a polynomial model:

Y = a1(X) + a2(X**2) + a3(X**3) + b1(Z) + b2(Z**2) + c

Finally (for now, anyway), what motivates the model that you want to fit?

[deleted_user]

i have data with one variable Y that changes depending on X and Z. But this change is not linear. I want to find the best fit curve and equation.

[deleted_user]

The values of X, Y and Z involve some negative values also and secondly the values are like 0.9,... -0.04,... 1.05