Originally posted by: JFYY_yaohua_tang

hello, everyone.

I have thousands of constraints, and I need to get their coefficients for each variable in each constraints, following is a example.

variables are x1 x2 x3 x4

constraint are 3*x1 + x3 + 5*x4 > 0

and what I need is a vector 3,0,1,5.

Is there any easy way to finish such a job?

thanks.
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Originally posted by: SystemAdmin

What API do you use (C, C++, Java, ...)?
Do you need the value 0 in the vector in your example or is it OK to return a vector that has only the non-zero elements?
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Originally posted by: JFYY_yaohua_tang

I need the 0, because I need to know the direction of the half plane indicated by the constraint.

I am using C++.

thanks.
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Originally posted by: SystemAdmin

Using an IloExpr::LinearIterator you can iterate over the non-zero terms of an IloRange:

IloExpr expr = range.getExpr(); 

for (IloExpr::LinearIterator l = expr.getLinearIterator(); l.ok(); ++l) 
{ std::cout << l.getCoef() << 
" * " << l.getVar() << std::endl; 
}

Since you also need the zero entries an probably also a particular order of the variables you need to do more. Assuming you have all your variables in an IloNumArray x you could store the non-zero coefficients in a map and then do something like this (untested code)

// Compare instances of IloNumVar by their extractable id. struct LessIloNumVar 
{ bool operator()(IloNumVar const& v1, IloNumVar const& v2) 

const 
{ 

return v1.getId() < v2.getId(); 
} 
};   
// Iterate over expression and store non-zero coefficients in a map. typedef std::map<IloNumVar,IloNum,LessIloNumVar> VarMap; VarMap varmap; IloExpr expr = range.getExpr(); 

for (IloExpr::LinearIterator l = expr.getLinearIterator(); l.ok(); ++l) 
{ 
// If the variable is already in the map then we just update the 
// coefficient. Otherwise we insert the variable into the map. VarMap::iterator it = varmap.find(l.getVar()); 

if ( it == varmap.end() ) varmap.insert(VarMap::value_type(l.getVar(), l.getCoef())); 

else it->second += l.getCoef(); 
}   
// Iterate over all variables and fetch their coefficients from the map. 
// If a variable is not in the map then its coefficient is 0. IloNumArray vec(x.getEnv()); 

for (IloInt i = 0; i < x.getSize(); ++i) 
{ VarMap::const_iterator it = varmap.find(x[i]); vec.add(it == varmap.end() ? 0 : it->second); 
}   
// vec is now the vector you are looking for.

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Originally posted by: JFYY_yaohua_tang

thanks so much , I have test your program and it works quit well.
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