[Ipopt] A maximization problem returns a minimum

Paul Smith phhs80 at gmail.com
Thu Jun 17 11:39:39 EDT 2010

Dear All,

I am running this simple model through AMPL and Ipopt 3.8.0:

var x >= 0;

let x := 0.5;

maximize F:	
   -16 * x * (x-1) * (2*x - 1)^2;

subject to R1:
   x <= 1;

Ipopt returns the following solution:

«EXIT: Optimal Solution Found.

Ipopt 3.8.0: Optimal Solution Found

suffix ipopt_zU_out OUT;
suffix ipopt_zL_out OUT;
ampl: display F, x;
F = 0
x = 0.5».

However the returned solution is a minimum and NOT a maximum. What am
I not understanding?

Thanks in advance,


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