Hello;

I modeled the following simple IP problem in Gams, but the solutions given by the Cplex solver and Xpress solver are strangely different. I mean the Cplex solver came up with only a feasible solution (3,3)[z=39] and not an optimal solution, but the right answer is (5,0)[z=40] that Xpress solver gives us.

I want to know what the problem is and how it can be solved.

Max z=8x+5y

St: x+y<=6

9x+5y<=45

x,y are integer and non-negative

Regard,

Anvar

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Hi Hesam

I think you manipulated the solver setting. I suggest you to reset the solver setting and whenever

you need to change solver, use the following command before solve statement:

Option lp=Solver_name;

The best and exact solution of your problem is:

x=3.75;

y=2.25;

z=41.25;

which is obtained by using Cplex;

On Fri, Nov 8, 2013 at 11:15 PM, hesameddin anvar wrote:

Hello;

I modeled the following simple IP problem in Gams, but the solutions given by the Cplex solver and Xpress solver are strangely different. I mean the Cplex solver came up with only a feasible solution (3,3)[z=39] and not an optimal solution, but the right answer is (5,0)[z=40] that Xpress solver gives us.

I want to know what the problem is and how it can be solved.

Max z=8x+5y

St: x+y<=6

9x+5y<=45

x,y are integer and non-negative

Regard,

Anvar

To unsubscribe from this group and stop receiving emails from it, send an email to gamsworld+unsubscribe@googlegroups.com.

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Hello,

Please try this piece of code, it gives z=40 at (5,0).

I guess the option *optcr* is missed in your run.

HTH,

Yan

- –

integer variables x, y;

variable z;

equation e1, e2, e3;

e1… z =E= 8*x+5*y;

e2… x+y =L= 6;

e3… 9*x+5*y =L= 45;

model tmp /all/;

x.lo = 0;

y.lo = 0;

option optcr=0;

option mip=cplex;

solve tmp maxmizing z using mip;

- –

å‘ä»¶äººï¼š hesameddin anvar

å‘é€æ—¶é—´ï¼š 2013-11-10 01:20:36

æ”¶ä»¶äººï¼š gamsworld

æŠ„é€ï¼š

ä¸»é¢˜ï¼š Cplex solver doesn’t come up with optimal solution

Hello;

I modeled the following simple IP problem in Gams, but the solutions given by the Cplex solver and Xpress solver are strangely different. I mean the Cplex solver came up with only a feasible solution (3,3)[z=39] and not an optimal solution, but the right answer is (5,0)[z=40] that Xpress solver gives us.

I want to know what the problem is and how it can be solved.

Max z=8x+5y

St: x+y<=6

9x+5y<=45

x,y are integer and non-negative

Regard,

Anvar

Reply-to: gamsworld@googlegroups.com

Thanks Ryan

On Monday, November 11, 2013 7:32:30 AM UTC+3:30, Ryan Ren wrote:

Hello,

Please try this piece of code, it gives z=40 at (5,0).

I guess the option *optcr* is missed in your run.

HTH,

Yan

- –

integer variables x, y;

variable z;

equation e1, e2, e3;

e1… z =E= 8*x+5*y;

e2… x+y =L= 6;

e3… 9*x+5*y =L= 45;

model tmp /all/;

x.lo = 0;

y.lo = 0;

option optcr=0;

option mip=cplex;

solve tmp maxmizing z using mip;

- –

å‘ä»¶äººï¼š hesameddin anvar

å‘é€æ—¶é—´ï¼š 2013-11-10 01:20:36

æ”¶ä»¶äººï¼š gamsworld

æŠ„é€ï¼š

ä¸»é¢˜ï¼š Cplex solver doesn’t come up with optimal solution

Hello;

I modeled the following simple IP problem in Gams, but the solutions given by the Cplex solver and Xpress solver are strangely different. I mean the Cplex solver came up with only a feasible solution (3,3)[z=39] and not an optimal solution, but the right answer is (5,0)[z=40] that Xpress solver gives us.

I want to know what the problem is and how it can be solved.

Max z=8x+5y

St: x+y<=6

9x+5y<=45

x,y are integer and non-negative

## Regard,

Anvar

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