Cplex solver doesn't come up with optimal solution

GAMS
1

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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2

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

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3

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= 8x+5y;
e2… x+y =L= 6;
e3… 9x+5y =L= 45;

model tmp /all/;

x.lo = 0;
y.lo = 0;

option optcr=0;
option mip=cplex;
solve tmp maxmizing z using mip;

  • –


    发件人： hesameddin anvar
    发送时间： 2013-11-10 01:20:36
    收件人： gamsworld
    抄送：
    主题： 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

4

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= 8x+5y;
e2… x+y =L= 6;
e3… 9x+5y =L= 45;

model tmp /all/;

x.lo = 0;
y.lo = 0;

option optcr=0;
option mip=cplex;
solve tmp maxmizing z using mip;

  • –


    发件人： hesameddin anvar
    发送时间： 2013-11-10 01:20:36
    收件人： gamsworld
    抄送：
    主题： 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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