Infeasibility & entries skipped

GAMS
1

Hi :smiley: I have some problems with my gams model about infeasibility and “entries skipped”. First of all what are the meanings of these? In 3 of 12 equations i have found “**** LHS=0, Infes=1****” “**** LHS=0, Infes=68.9****” “**** LHS=0, Infes=11800****”. These numbers are obviously those I have insered before in the model. Can this type of alert give problems to results? How can I fix it? In others 5 equations i have found “remaining 6(or another number) entries skipped”, what is the meaning? How can i fix it?

Thanks to everyone :smiley: :smiley:

2

Hi,

You are referring to the equation listing which provides information about the generated model before it is solved.
Infes=… indicates that the equation is infeasible for the given start point (i.e. based on the current levels of variables when the model is generated).
“remaining … entries skipped” refers to expanded equations not shown in the equation listing. If you have a set i with 10 elements i1, i2, …, i10 and an equation eq(i), by default the equation listing will only show the first three equations eq(i1), eq(i2), eq(i3). You can change that via option limrow.

I hope this helps!

Fred

3

Thanks for “entries skipped” explaination. Very kind.
But, I didn’t understand infeasible issue. If I have this type of problem in which way can I solve it?
May I change my input data?
Can be this a problem about a large range in values?
Many thanks

4

There is no problem. It is usual that the initial point is not feasible.
Look for example at the trnsport model.

The equation listing shows

---- demand  =G=  satisfy demand at market j

demand(new-york)..  x(seattle,new-york) + x(san-diego,new-york) =G= 325 ; (LHS = 0, INFES = 325 ****)
     
demand(chicago)..  x(seattle,chicago) + x(san-diego,chicago) =G= 300 ; (LHS = 0, INFES = 300 ****)
     
demand(topeka)..  x(seattle,topeka) + x(san-diego,topeka) =G= 275 ; (LHS = 0, INFES = 275 ****)

This is expected because by default x.l() is equal to zero.

I hope this helps!

Fred