Originally posted by: BCDS_Daniel_Underwood

This code works:

dvar float x;
minimize x^2;
subject to
{
    x <= 10;
    x >= 2;
}

But this code does not work:

dvar float x;
minimize 1/x;
subject to
{
    x <= 10;
    x >= 2;
}

I don't understand why the second code example fails? Are decision variables not permitted in the denominator of fractions? If not, why aren't they?
#DecisionOptimization
#OPLusingCPLEXOptimizer

Hi,

indeed the cplex engine cannot handle such an objective since it is not linear nor quadratic.
But you can use the CP optimizer engine. (You will then need a variable change)

using CP;
 
dvar int x2 in -10000..10000;
 
dexpr float x=x2/1000;
 
dexpr  float obj=1/x;;
minimize obj;
subject to
{
    x <= 10;
    x >= 2;
}

will give x=10

Regards
#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: BCDS_Daniel_Underwood

Thanks a lot!
#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: NRouge

Hi,

I'm new to Cplex and I'm facing same error. I have this problem:

 

int noport=2;
int noship=1;range port=1..noport;
range ship=1..noship;

...

int d[port,port]=...;

...

dvar int y[port,port,ship];

dvar int z[ship];

 

forall (i in 1..noport-1,j in i+1..noport,k in ship)
y[i,j,k] <= (d[i,j])/(z[k])* sum(p in i..j-1) x[p,j,k];

 

"(d[i,j])/(z[k])" this part cause the error "Function operator/(int,dvar int) not available in context CPLEX.".

 

It works fine if it is (d[i,j])*(z[k]), but it doesn't work with the division and I don't know why. I attached mod file of my work  for more details.

Please help. Thank you

 

#DecisionOptimization
#OPLusingCPLEXOptimizer

Hi,

same as 5 years ago.

Dividing by a decision variable is not linear.

So can you try with 

using CP;

regards

#DecisionOptimization
#OPLusingCPLEXOptimizer