You have nonlinear constraints on the parameters.  Take a look at constrained optimization algorithms in packages "alabama" or "Rsolnp" that can handle non-linearly constrained optimization problems.

Ravi

Ravi Varadhan, Ph.D.
Assistant Professor
The Center on Aging and Health
Division of Geriatric Medicine & Gerontology
Johns Hopkins University
rvaradhan@jhmi.edu<mailto:rvaradhan@jhmi.edu>
410-502-2619


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