ipopt solver external function that computes the gradient of the objective for CUTEr.
g = ipopt_grobj(x)
A vector, the current value of the unknown
A vector, the current value of the objective function
This function computes the value of the gradient of the objective at the point
x
for the current CUTEr problem according to
the ipopt
requirements.
It includes a cpu time limitation to cancel the resolution if the cpu time exceeds 3600s.