I am running a series of state-space density-independent and -dependent population models in PROC MIXED. I have reviewed the literature and found out how to do the gompertz and exponential growth models. I am still struggling to fit a random walk and ricker model. PROC MIXED does not have a restrict statement. How do I restrict parameters in PROC MIXED? Below is the code for the gompertz model:

ODS OUTPUT FITSTATISTICS=FIT_GOMPERTZ2;

ODS OUTPUT CovParms=GOMPERTZ_PARMS2;

PROC MIXED METHOD=REML ALPHA=.05 NOITPRINT NOINFO DATA=FISH_DENSITY;

BY REGION SITE SPECIES;

CLASS TIME;

MODEL LOG_Nt=LOG_Nt_Minus1 / s outp=pred;

RANDOM TIME;

REPEATED / TYPE=AR(1) SUBJECT=INTERCEPT;

ESTIMATE 'INTERCEPT' INTERCEPT 1;

RUN;