search for: y2error

Hello! I have a set of data of the form (x, y1, y2) where x is the independent variable and (y1, y2) is the response pair. The model is some messy non-linear function: (y1, y2) = f(x; param1, param2, ..., paramk) + (y1error, y2error) where the parameters param1, ..., paramk are to be estimated, and I'll assume the errors to be normal for sake of simplicity. If there were only one response per input, I would use the nls() function, but what can I do in this case? Many thanks, Julian