test(){ # use covariate statement to declare custom X variable covariate(X) # model equation Y = Alpha / (1 + exp(Beta-Gamma*X)) # observed Y and error model error(YEps = 1) observe(YObs(X) = Y + YEps) # Fixed effects parameters with initial estimates fixef(Alpha = c(, 50, )) fixef(Beta = c(, 1, )) fixef(Gamma = c(, 1, )) }