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Posted 06-22-2009 05:30 PM
(1854 views)
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
Y= a(x) + b(z)+c,
X and Z may have some powers (n) also.How to do it? Please guide
3 REPLIES 3
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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?
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?
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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.
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The values of X, Y and Z involve some negative values also and secondly the values are like 0.9,... -0.04,... 1.05