Problem with ignoring GAMS constraints

GAMS
1

Dear Sir or Madam,

I have developed a mid-sized minimization model (176 variables, 4180 constraints).

When I execute the model on different non-linear solvers I get results, which I plug it into an excel spreadsheet for analysis.

My problem is that my more complicated constraints are not honored (i.e. when i insert the values of x1, y1, x56 and y56 into the equation it is LESS THAN 54). Example

c407… (x1-x56) * (x1-x56) + (y1-y56) * (y1-y56) =g= 54 ;

Simple constraints are honored. Example

c12… x12 =g= 3 ;

How do I instruct the solver to honor the constraints exactly as they are written (a hard constraint) and if there is no solution, simply to say it is infeasible.

Thank you for your effort.

Chicago

2

Did you check the model/solve status before you report things back to Excel? The solver might have told you that the model is (locally) infeasible.

-Michael

3

Yes. I’m using the NEOS server at the University of Wisconsin. There are a number of solvers and I test them all. Several literally come back saying optimized. I know because others say “too many iterations”, so I take the final values and use them as initial values in the next run.

4

This seems odd. Did you get to the buttom of this, Chicago?

5

Unfortunately no. I tried changing the constraints from quadratics to absolute values to simplify them even though a less precise solution would result. Similar output.