Originally posted by: Zefeng

Hi, I encountered a strange problem. I was using CP to solve a problem and feasible solutions could be found. But when I changed the objective, with the other parts unchanged, no solutions could be found. I think changing the objective has nothing to do with the solution space, so such a thing should not happen. What might be the reason? 

#DecisionOptimization
#OPLusingCPLEXOptimizer

Hi,

you get no solution because of time limit ?

If yes, can you increase the time limit ?

regards

#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: Zefeng

In fact, I did not set time limit for the problem. 

These are the .mod file and the .dat file. 

.mod file:

using CP;

int numfac=...;
int xnumgrid=...;
int ynumgrid=...;

int gridlength=...;
int gridwidth=...;

int roadwidth=...;

int faclength[i in 1..numfac][j in 1..2]=...;

float cost[i in 1..numfac][j in 1..numfac]=...;

dvar interval facits[i in 1..numfac][j in 1..2] size faclength[i][j];

dvar boolean atx[i in 1..numfac][x in 1..xnumgrid];
dvar boolean aty[i in 1..numfac][y in 1..ynumgrid];

int ust[y in 1..ynumgrid]=y*(roadwidth+gridwidth);
int dst[y in 1..ynumgrid]=y*(roadwidth+gridwidth)-gridwidth;
int rst[x in 1..xnumgrid]=x*(roadwidth+gridlength);
int lst[x in 1..xnumgrid]=x*(roadwidth+gridlength)-gridlength;

dexpr int uedge[i in 1..numfac]=sum(y in 1..ynumgrid) ust[y]*aty[i][y];
dexpr int dedge[i in 1..numfac]=sum(y in 1..ynumgrid) dst[y]*aty[i][y];
dexpr int redge[i in 1..numfac]=sum(x in 1..xnumgrid) rst[x]*atx[i][x];
dexpr int ledge[i in 1..numfac]=sum(x in 1..xnumgrid) lst[x]*atx[i][x];

dvar boolean direc[i in 1..numfac];
dexpr int ufac[i in 1..numfac]=endOf(facits[i][1])*(1-direc[i])+endOf(facits[i][2])*direc[i];
dexpr int dfac[i in 1..numfac]=startOf(facits[i][1])*(1-direc[i])+startOf(facits[i][2])*direc[i];
dexpr int rfac[i in 1..numfac]=endOf(facits[i][2])*(1-direc[i])+endOf(facits[i][1])*direc[i];
dexpr int lfac[i in 1..numfac]=startOf(facits[i][2])*(1-direc[i])+startOf(facits[i][1])*direc[i];

dvar boolean fac[i in 1..numfac];
dexpr int fx[i in 1..numfac]=(direc[i])*(startOf(facits[i][1])+endOf(facits[i][1])) div 2+
    (1-direc[i])*((endOf(facits[i][2])+roadwidth div 2)*fac[i]+(startOf(facits[i][2])-roadwidth div 2)*(1-fac[i]));
dexpr int fy[i in 1..numfac]=(1-direc[i])*(startOf(facits[i][1])+endOf(facits[i][1])) div 2+
    (direc[i])*((endOf(facits[i][2])+roadwidth div 2)*fac[i]+(startOf(facits[i][2])-roadwidth div 2)*(1-fac[i]));

dexpr int samex[i in 1..numfac][j in 1..numfac]=sum(x in 1..xnumgrid) (atx[i][x]*atx[j][x]);
dexpr int samey[i in 1..numfac][j in 1..numfac]=sum(y in 1..ynumgrid) (aty[i][y]*aty[j][y]);

dexpr int spcountx[i in 1..numfac][j in 1..numfac]=samex[i][j]*direc[i]*direc[j]*(fy[i]!=fy[j]);
dexpr int spcounty[i in 1..numfac][j in 1..numfac]=samey[i][j]*(1-direc[i])*(1-direc[j])*(fx[i]!=fx[j]);

dexpr int absx[i in 1..numfac][j in 1..numfac]=(fx[i]+fx[j]-ledge[i]-redge[i]>=0)*(fx[i]+fx[j]-ledge[i]-redge[i])
                                               +(fx[i]+fx[j]-ledge[i]-redge[i]<0)*(ledge[i]+redge[i]-fx[i]-fx[j]);
dexpr int absy[i in 1..numfac][j in 1..numfac]=(fy[i]+fy[j]-dedge[i]-uedge[i]>=0)*(fy[i]+fy[j]-dedge[i]-uedge[i])
                                               +(fy[i]+fy[j]-dedge[i]-uedge[i]<0)*(dedge[i]+uedge[i]-fy[i]-fy[j]);

dexpr int spdistancex[i in 1..numfac][j in 1..numfac]=roadwidth-absx[i][j]-ledge[i]+redge[i];
dexpr int spdistancey[i in 1..numfac][j in 1..numfac]=roadwidth-absy[i][j]-dedge[i]+uedge[i];

/*    after adding search phases, both objective 1 and objective 2 has solutions
execute {
   cp.param.TimeMode = "ElapsedTime";
   cp.param.TimeLimit = 6000;
   var f = cp.factory;
   cp.setSearchPhases(f.searchPhase(atx),f.searchPhase(aty),
                           f.searchPhase(direc),f.searchPhase(fac),
                           f.searchPhase(facits));
}
*/

/*    objective 1, no solutions found with this objective
minimize sum(i,j in 1..numfac:i<j) cost[i][j]*(
    abs(fx[i]-fx[j])*(1-spcountx[i][j])+spdistancex[i][j]*spcountx[i][j]+
    abs(fy[i]-fy[j])*(1-spcounty[i][j])+spdistancey[i][j]*spcounty[i][j]
);
*/

//    objective 2, solutions can be found with this objective
minimize sum(i,j in 1..numfac:i<j) cost[i][j]*(
    abs(fx[i]-fx[j])*(1-spcountx[i][j])+
    abs(fy[i]-fy[j])*(1-spcounty[i][j])
);
//

subject to
{
    forall(ordered i,j in 1..numfac)
        or(k in 1..2) (direc[i]==direc[j])*overlapLength(facits[i][k],facits[j][k])+
                      (direc[i]!=direc[j])*overlapLength(facits[i][k],facits[j][3-k])==0;

    forall(i in 1..numfac){
        sum(j in 1..xnumgrid) atx[i][j]==1;
        sum(j in 1..ynumgrid) aty[i][j]==1;
        ufac[i]<=uedge[i];
        dfac[i]>=dedge[i];
        rfac[i]<=redge[i];
        lfac[i]>=ledge[i];
    }

    forall(i in 1..numfac){
        (endOf(facits[i][2])*fac[i]+startOf(facits[i][2])*(1-fac[i]))==
        (uedge[i]*fac[i]+dedge[i]*(1-fac[i]))*direc[i]+
        (redge[i]*fac[i]+ledge[i]*(1-fac[i]))*(1-direc[i]);
    }
}

.dat file:

numfac=6;
xnumgrid=1;
ynumgrid=1;
gridlength=1000000;
gridwidth=1000000;
roadwidth=100000;

faclength=[
[62150 105700]
[76400 369000]
[147000 39300]
[354950 178550]
[179450 370200]
[323600 347050]
];

cost=[
[0 7.092 3.7 9.366 2.613 4.305]
[7.092 0 0.038 9.803 5.282 5.054]
[3.7 0.038 0 0.582 3.428 8.622]
[9.366 9.803 0.582 0 6.153 1.28]
[2.613 5.282 3.428 6.153 0 0.525]
[4.305 5.054 8.622 1.28 0.525 0]
];

#DecisionOptimization
#OPLusingCPLEXOptimizer

Hi,

then can you post your model here so that other users could have a look ?

regards

#DecisionOptimization
#OPLusingCPLEXOptimizer