how to specify tolerance for cost while using grey box modeling in system identification

I am trying to identify parameters in a nonlinear model. I am using nonlinear grey box model and 'pem' function for that purpose. I want to specify the tolerance for the cost function when using pem, which uses Trust-Region Reflective Newton method. There is a option in nlgr.Algorithm.Tolerance but it specifies the tolerance for the change in the parameter not the cost function. I really appreciate it if any one can guide me in this issue.

[yem]

hii i have the same problem now i want to identify parameters in a non linear model with Newton methods..I really appreciate it if you help me