Import IPOPT version 3.11.5 as math/ipopt

Ipopt (Interior Point OPTimizer, pronounced eye-pea-Opt)
is a software package for large-scale nonlinear optimization.
It is designed to find (local) solutions of mathematical
optimization problems of the form

min_{x in R^n} f(x)

s.t.  g_L <= g(x) <= g_U
      x_L <=  x   <= x_U

where f(x): R^n --> R is the objective function,
and g(x): R^n --> R^m are the constraint functions.
The vectors g_L and g_U denote the lower and upper bounds on the
constraints, and the vectors x_L and x_U are the bounds on the
variables x. The functions f(x) and g(x) can be nonlinear and
nonconvex, but should be twice continuously differentiable.
Note that equality constraints can be formulated in the above
formulation by setting the corresponding components of g_L and
g_U to the same value.

Ipopt is part of the  COIN-OR Initiative.