Hi I´m using PROC SYSLIN in SAS program to set a system of allometric equations to predict biomass. 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´m taking several equations defined by Parresol to predict the biomass of stem, bark, crown and total biomass, for example: Biomass (stem) =a 0 +a 1 *(D 2 *H)+ε Biomass (bark) =b 0 +b 1 *(D 2 *H)+ε Biomass (crown) =c 0 +c 1 *(GRANDE)+C 2 *H+ε Biomass (total) =d 0 +d 1 *(D 2 *H)+d 2 *(GRANDE)+d 3 *H+ε And the equations of the error variance, wich will be used as weights are: σ 2 e(stem)=(D 2 *H) 1.95 , σ 2 e (bark)=(D 2 ) 1.745 σ 2 e (crown)=(GRANDE) 1.646 *exp(-0.0046H 2 ) σ 2 e (total)=(D 2 *H) 1.844 "D", "H" and "GRANDE" are exogenous variables. I had no problems with a restricted SUR fit( without weights) in SYSLIN, the procedure is simple if the restrictions are well established through SRESTRICT. DATA ONE; SET PARRESOL; X11=D**2*H; W1=1/((D**2*H)**1.95); X21=D**2*H; W2=1/((D**2*H)**1.745); X31=GRANDE; X32=H; W3=1/((GRANDE**1.646)*(EXP(-0.00406*H**2))); X41=D**2*H; X42=GRANDE; X43=H; W4=1/((D**2*H)**1.844); Y1=WOOD; Y2=BARK; Y3=CROWN; Y4=TREE; PROC SYSLIN DATA=ONE SUR; PWOOD: MODEL Y1 = X11; PBARK: MODEL Y2 = X21; PCROWN: MODEL Y3 = X31 X32; TOTAL: MODEL Y4 = X41 X42 X43; SRESTRICT TOTAL.INTERCEPT=PWOOD.INTERCEPT+PBARK.INTERCEPT+PCROWN.INTERCEPT, TOTAL.X41=PWOOD.X11+PBARK.X21, TOTAL.X42=PCROWN.X31, TOTAL.X43=PCROWN.X32; RUN; 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.

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