[R] HELP ON NON-LINEAR MIXED MODEL

[Popoola Daniel]

Good Morning Sir/Ma,
I am POPOOLA DANIEL a Forest Biometrician in making from the University of Ibadan, Ibadan Nigeria. Please Sir/Ma I am having issues on performing Non-linear mixed model on R (using maximum likelihood approach). I am trying to input four different measured variables which are basal area, diameter at breast height, Dominant height,quadratic mean diameter as a function for height prediction on equation. But I have not been able to get through with the model.

Please I need your  candid options on how to go about this. Other useful tips on Codes entering for data analysis in R environment will also be appreciated . 

Thanks in anticipation to your reply.