 ××××××× Anonymous, undated    == x4+y4+xy  & (0,0)==   Sorry I can't answer the question posted by a non-signer. I have a different question myself.  I am confused. x4+y4+xy  seems to have  a global minimum on (0,0), according to my contour plot. Yet, the hessian (ie [0 1, 1 0]) has a positive and a negative eigenvalue (1 and -1). Hence it should be a saddle point, right? I am confused... I would hope every saddle point looks like the critical point (0,0) in the function x2-y2  