[Coin-ipopt] Bug with derivative checker in IPOPT 3.3.3

[Peter Carbonetto]

I believe I've discovered a bug in IPOPT version 3.3.3 that does not 
occur in version 3.3.1.

I modified the Ipopt/examples/hs071_cpp/hs071_main.cpp file so that the 
options now include the line

   app->Options()->SetStringValue("derivative_test","first-order");

When I run this example hs071_cpp the derivative checker, the solver 
initially requests to evaluate the point in eval_f:

x = [ 1.0000000000775426
       1.0000000008465582
       1.0000000015549682
       1.0000000006258227 ]

But the initial point given is x = [1 5 5 1]. This behaviour does not 
occur in version 3.3.1 of the software package. I didn't try the latest 
(non-public) version, and I will do that next. If anyone manages to 
reproduce this buggy behaviour, it would be good to know.

Peter Carbonetto
Ph.D. Candidate
Dept. of Computer Science
University of British Columbia