LpBase::Expr Class Reference

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.

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

or you can also iterate through its elements.

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

(This code computes the primal value of the expression).

• 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 dereference operator (unary *)

*e=12;
double c=*e;

See Also

Constr

#include <lemon/lp_base.h>

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

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

Public Member Functions
	Expr ()
	Default constructor.
	Expr (const Col &c)
	Construct an expression from a column.
	Expr (const Value &v)
	Construct an expression from a constant.
Value	operator[] (const Col &c) const
	Returns the coefficient of the column.
Value &	operator[] (const Col &c)
	Returns the coefficient of the column.
void	set (const Col &c, const Value &v)
	Sets the coefficient of the column.
Value &	operator* ()
	Returns the constant component of the expression.
const Value &	operator* () const
	Returns the constant component of the expression.
void	simplify (Value epsilon=0.0)
	Removes the coefficients which's absolute value does not exceed epsilon. It also sets to zero the constant component, if it does not exceed epsilon in absolute value.
void	clear ()
	Sets all coefficients and the constant component to 0.
Expr &	operator+= (const Expr &e)
	Compound assignment.
Expr &	operator-= (const Expr &e)
	Compound assignment.
Expr &	operator*= (const Value &v)
	Multiply with a constant.
Expr &	operator/= (const Value &c)
	Division with a constant.

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

Constructor & Destructor Documentation

Expr ( )

inline

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

Expr ( const Col &  c )

inline

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

Expr ( const Value &  v )

inline

Construct an expression, which's constant component is v.