When I fit the mixed effect model I got this warning:
1: In checkConv(attr(opt, "derivs"), opt\$par, ctrl = control\$checkConv, : Model failed to converge with max|grad| = 0.00202181 (tol = 0.001, component 1)
2: In checkConv(attr(opt, "derivs"), opt\$par, ctrl = control\$checkConv, : Model is nearly unidentifiable: very large eigenvalue - Rescale variables?
I think it is telling me the optimization does not converge, (gradient is not close zero). So I listed more details about the optimization.
Could any one tell me why we have a large number in Hessian matrix? what is happening there?