Hi,
I´m using PROC SYSLIN in SAS program to set a system of equations to predict biomass in Acacia spp. My goal is to make a weighted restricted SUR fit (or WRSUR, like Parresol, 1999) as there is correlation between the errors of the equations. I have different equations to predict the biomass of stem, foliage, branches and total biomass, each with different functions of variance, for example:
Biomass(stem)=a0+a1*(DAC2*H)+ε
Biomass(branches)=b0+b1*(DAC2*H)+ε
Biomass(foliaje)=c0+c1*(DAC2)+ε
Biomass(total)=d0+d1*(DAC2)+d2*(DAC2*H)+ε
And the equations of the error variance, wich will be used as weights are:
σ2e(stem)=(DAC2*H)1.806,
σ2e (branches)=(DAC2)1.8744
σ2e (foliaje)=(DAC2*H)1.607
σ2e (total)=(DAC2*H)1.998
DAC=Diameter at the neck of the tree
H=Total tree height
I had no problems with a restricted SUR fit in SYSLIN, the procedure is relatively simple if the restrictions are well established through SRESTRICT. However, it seems that I have problems syntax to perform a WRSUR, since I do not know how to indicate the weights for the corresponding equation. I just know I should define the four weights in the input data set, but then not as assigning weights to each equation corresponding to conduct a weighted restricted SUR fit. Also, I have to define a variance-covariance previously in SYSLIN?. Can anyone help me with the correct syntax?, I appreciate a lot since I`m stuck.
May be it is easy to do a regression relation between different treats and actual yield.
I asked this question once, you can check te answers. Most of the answers suggested using R. I used Parresol data as test data abd the results wre different. Finally, I Did the analyzes in statistica 12. This analyze is so user-friendly in this software.
https://www.researchgate.net/post/How_to_calculate_nonlinear_seemingly_unrelated_regression_NSUR
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