Control the Iteration in nlme()
USAGE: 
nlme.control(maxiter = 50, pnls.maxiter = 7, lme.maxiter = 50,
             minscale = 0.001, tolerance = 0.001,
             pnls.tolerance = 0.001, lme.tolerance = 1e-06,
             return.object = F)
OPTIONAL ARGUMENTS:
maxiter:
maximum number of iterations during fit. Default is 50.
pnls.maxiter:
maximum number of iterations during penalized nonlinear least squares (PNLS) step. Default is 7.
lme.maxiter:
maximum number of iterations during linear mixed effects (LME) step. Default is 50.
minscale:
minimum factor by which to shrink the default step size in an attempt to decrease the sum of squares in the PNLS step. Default 0.001.
tolerance:
tolerance for the convergence criterion in the algorithm. Default is 0.001.
pnls.tolerance:
tolerance for the convergence criterion in the PNLS step. Default is 0.001.
lme.tolerance:
tolerance for the convergence criterion in the LME step, passed as the rel.tolerance argument to ms (see documentation on that function). Default is 0.000001.
return.object:
if T (TRUE) the fitted object is returned by nlme() when the maximum number of iterations (maxiter) is attained without convergence. Default is F.
VALUE:
A list containing components for each of the possible arguments, either the value supplied by the user or the default. Its value is used as the control argument to the nlme() function.
SEE ALSO:
nlme , nlme.formula , nlme.nlsList .
EXAMPLES: 
# increase the maximum number of iterations in the PNLS step and return the
# object when maximum number of iterations is attained without convergence
nlme.control(pnls.maxiter = 20, return.object = T)