About multiobjective problem

[vjavier77]

Hi
I´m trying to solve a multi objective optimization problem using
knitro in AMPL, like this:

minimize generation_cost :
sum{k in BUS : bus_type[k] == 2 || bus_type[k] == 3} (costA[k] +
costB[k]*PG[k] + costC[k]*(PG[k])^2);

minimize deltaPL :
sum{i in BUS} alfa*dir[i]*Pload0[i];

subject to ......(set of constraints)

and when I try to run the .mod file I obtain the following message

exit code 1
<BREAK>

What does it means?
I checked the knitro 5.1 user manual and I didn't find any information
about it.

Thanks in advance

[Richard Waltz]

Hi,

KNITRO can only accept models with one objective function. The error
is probably coming from the AMPL interface. It is probably designed
to break and exit if the model contains more than one objective
function. I thought an error message would also be printed in this
case to describe the problem but I need to check on this. The error
message may only appear if you run the *.nl file outside of AMPL. At
any rate, you will need to change your model so that it only has one
objective if you wish to use KNITRO.

-Richard Waltz