LpBase::DualExpr Class Reference

Detailed Description

This data structure represents a column of the matrix, thas is it strores a linear expression of the dual variables (Rows).

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

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

or you can also iterate through its elements.

double s=0;
for(LpBase::DualExpr::ConstCoeffIt i(e);i!=INVALID;++i)
  s+=*i;

(This code computes the sum of all coefficients).

• Numbers (double's) and variables (Rows) directly convert to an DualExpr and the usual linear operations are defined, so

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

  are valid DualExpr dual expressions. The usual assignment operations are also defined.

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

See Also

Expr

#include <lemon/lp_base.h>

Classes
class	CoeffIt
	Iterator over the expression. More...
class	ConstCoeffIt
	Iterator over the expression. More...

Public Types
typedef LpBase::Row	Key
	The key type of the expression.
typedef LpBase::Value	Value
	The value type of the expression.

Public Member Functions
	DualExpr ()
	Default constructor.
	DualExpr (const Row &r)
	Construct an expression from a row.
Value	operator[] (const Row &r) const
	Returns the coefficient of the row.
Value &	operator[] (const Row &r)
	Returns the coefficient of the row.
void	set (const Row &r, const Value &v)
	Sets the coefficient of the row.
void	simplify (Value epsilon=0.0)
	Removes the coefficients which's absolute value does not exceed epsilon.
void	clear ()
	Sets all coefficients to 0.
DualExpr &	operator+= (const DualExpr &e)
	Compound assignment.
DualExpr &	operator-= (const DualExpr &e)
	Compound assignment.
DualExpr &	operator*= (const Value &v)
	Multiply with a constant.
DualExpr &	operator/= (const Value &v)
	Division with a constant.

Related Functions
(Note that these are not member functions.)
LpBase::DualExpr	operator+ (const LpBase::DualExpr &a, const LpBase::DualExpr &b)
	Addition.
LpBase::DualExpr	operator- (const LpBase::DualExpr &a, const LpBase::DualExpr &b)
	Substraction.
LpBase::DualExpr	operator* (const LpBase::DualExpr &a, const LpBase::Value &b)
	Multiply with constant.
LpBase::DualExpr	operator* (const LpBase::Value &a, const LpBase::DualExpr &b)
	Multiply with constant.
LpBase::DualExpr	operator/ (const LpBase::DualExpr &a, const LpBase::Value &b)
	Divide with constant.

Constructor & Destructor Documentation

DualExpr ( )

inline

Construct an empty expression, the coefficients are initialized to zero.

DualExpr ( const Row &  r )

inline

Construct an expression, which has a term with r dual variable and 1.0 coefficient.