Refer to http://ab-initio.mit.edu/wiki/index.php/NLopt_Reference#Forced_termination
Equivalent in C API: nlopt_get_force_stop
The last force stop value.
See Implementation
Refer to http://ab-initio.mit.edu/wiki/index.php/NLopt_Reference#Forced_termination
Equivalent in C API: nlopt_get_force_stop