Expr Class Reference

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Detailed Description

This data structure stores a linear expression of the variables (Cols) and also has a constant component.

There are several ways to access and modify the contents of this container.

• Its it fully compatible with std::map<Col,double>, so for expamle if e is an Expr and v and w are of type Col, then you can read and modify the coefficients like these.

         e[v]=5;
         e[v]+=12;
         e.erase(v);
  

  or you can also iterate through its elements.

         double s=0;
         for(LpSolverBase::Expr::iterator i=e.begin();i!=e.end();++i)
           s+=i->second;
  

  (This code computes the sum of all coefficients).
• Numbers (double's) and variables (Cols) directly convert to an Expr and the usual linear operations are defined, so

         v+w
         2*v-3.12*(v-w/2)+2
         v*2.1+(3*v+(v*12+w+6)*3)/2
  

  are valid Expressions. The usual assignment operations are also defined.

         e=v+w;
         e+=2*v-3.12*(v-w/2)+2;
         e*=3.4;
         e/=5;
  

• The constant member can be set and read by constComp()

         e.constComp()=12;
         double c=e.constComp();
  

Note:

clear() not only sets all coefficients to 0 but also clears the constant components.

See also:

Constr

#include <lemon/lp_base.h>

Inherits std::map<Col,Value>.

List of all members.

Public Member Functions
	Expr ()
	Expr (const Key &v)
	Expr (const Value &v)
void	set (const Key &v, const Value &c)
Value &	constComp ()
const Value &	constComp () const
void	simplify ()
	Removes the components with zero coefficient.
void	simplify (double &tolerance)
	Removes the coefficients closer to zero than tolerance.
void	clear ()
	Sets all coefficients and the constant component to 0.
Expr &	operator+= (const Expr &e)
Expr &	operator-= (const Expr &e)
Expr &	operator*= (const Value &c)
Expr &	operator/= (const Value &c)
Related Functions
(Note that these are not member functions.)
LpSolverBase::Expr	operator- (const LpSolverBase::Expr &a, const LpSolverBase::Expr &b)
LpSolverBase::Expr	operator* (const LpSolverBase::Expr &a, const LpSolverBase::Value &b)
LpSolverBase::Expr	operator* (const LpSolverBase::Value &a, const LpSolverBase::Expr &b)
LpSolverBase::Expr	operator/ (const LpSolverBase::Expr &a, const LpSolverBase::Value &b)