https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47807#M2108 The values of X, Y and Z involve some negative values also and secondly the values are like 0.9,... -0.04,... 1.05 Sat, 27 Jun 2009 22:09:53 GMT deleted_user 2009-06-27T22:09:53Z https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47804#M2105 I have data with 3 variables X,Y,Z and i want to fit a model like ...<BR /> Y= a(x) + b(z)+c, <BR /> X and Z may have some powers (n) also.How to do it? Please guide Mon, 22 Jun 2009 21:30:07 GMT https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47804#M2105 deleted_user 2009-06-22T21:30:07Z https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47805#M2106 Your problem specification is incomplete. Let me respond by first asking a few questions.<BR /> <BR /> 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.<BR /> <BR /> Do you want to consider polynomial functions of X and Z? The model below is representative of a polynomial model:<BR /> <BR /> Y = a1(<B>X</B>) + a2(<B>X**2</B>) + a3<B>(X**3</B>) + b1(<B>Z</B>) + b2(<B>Z**2</B>) + c<BR /> <BR /> Finally (for now, anyway), what motivates the model that you want to fit? Fri, 26 Jun 2009 17:51:22 GMT https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47805#M2106 Dale 2009-06-26T17:51:22Z https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47806#M2107 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. Sat, 27 Jun 2009 22:07:07 GMT https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47806#M2107 deleted_user 2009-06-27T22:07:07Z https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47807#M2108 The values of X, Y and Z involve some negative values also and secondly the values are like 0.9,... -0.04,... 1.05 Sat, 27 Jun 2009 22:09:53 GMT https://communities.sas.com/t5/Statistical-Procedures/Curve-fitting-on-Data-with-three-variable-X-Y-Z/m-p/47807#M2108 deleted_user 2009-06-27T22:09:53Z