LinExpr

This class is used to represent linear expressions in the modeling interface of idol.

It consists in a set of linear terms which represent products of keys (typically, variables) and scalars.

Example

In this example, we create a linear expression representing the following linear expression.

\[3 x_0 + 2 x_1\]

auto x = model.add_vars(Dim<1>(2), 0, Inf, Continuous, "x");

LinExpr lin_expr = 3 * x[0] + 2 * x[1];

template<class Key = idol::Var>
class LinExpr : public idol::AbstractExpr<idol::Var, LinTerm<idol::Var>>

Template Parameters:

Key – the class representing keys

Public Functions

LinExpr() = default

LinExpr(const Key &t_key)

LinExpr(Constant &&t_factor, const Key &t_key)

LinExpr(const Constant &t_factor, const Key &t_key)

void set(const Key &t_key, const Constant &t_coefficient)

Sets the value of a key’s coefficient

The constant is copied.

Example:

LinExpr lin_expr;
lin_expr.set(x[0], -1);

Parameters:

• t_key – the key

• t_coefficient – the key’s coefficient

virtual void set(const Key &t_key, Constant &&t_coefficient) override

Sets the value of a key’s coefficient

The constant is moved.

Example:

LinExpr lin_expr;
lin_expr.set(x[0], -1);

Parameters:

• t_key – the key

• t_coefficient – the key’s coefficient

virtual const Constant &get(const Key &t_key) const override

Returns a key’s coefficient

Example:

LinExpr lin_expr = 2 * x[0] + 3 * x[1];

std::cout << lin_expr.get(x[0]) << std::endl; // output: 2

Parameters:

t_key – the key

Returns:

the key’s coefficient

virtual void remove(const Key &t_key) override

Sets the coefficient of a key to zero

This is equivalent to calling LinExpr<Key>::set with a zero coefficient.

Parameters:

t_key – the key

LinExpr fix(const Solution::Primal &t_primals) const

AbstractExpr<Key, IteratorOutputT, Hash, EqualTo> &operator+=(const AbstractExpr<Key, IteratorOutputT, Hash, EqualTo> &t_rhs)

Adds each term of t_rhs to the expression.

Zero entries are removed from the resulting expression.

Parameters:

t_rhs – the expression whose terms are to be added up.

Returns:

The object itself.

AbstractExpr<Key, IteratorOutputT, Hash, EqualTo> &operator-=(const AbstractExpr<Key, IteratorOutputT, Hash, EqualTo> &t_rhs)

Subtracts each term of t_rhs to the expression.

Zero entries are removed from the resulting expression.

Parameters:

t_rhs – The object whose terms are to be subtracted.

Returns:

The object itself.

AbstractExpr<Key, IteratorOutputT, Hash, EqualTo> &operator*=(double t_factor)

Multiplies every term of the expression by t_factor.

If t_factor equals zero with tolerance Tolerance::Sparsity, then the expression is emptied.

Parameters:

t_factor – The multiplying factor.

Returns:

The object itself.

AbstractExpr<Key, IteratorOutputT, Hash, EqualTo> &operator/=(double t_factor)

inline unsigned int size() const

Returns the size of the expression (i.e., number of non-zero entries which are currently stored).

Returns:

the size of the expression

inline bool empty() const

Returns true if and only if the size is zero.

Returns:

true if and only if the size is zero

inline const_iterator begin() const

Returns an iterator pointing to the first term of the expression.

Returns:

an iterator pointing to the first term of the expression

inline const_iterator end() const

Returns an iterator pointing to the end of the expression.

Returns:

an iterator pointing to the end the expression

inline void clear()

Removes all entries from the expression.

void round()

AbstractExpr multiply_with_precision(double t_factor, unsigned int t_n_digits)

AbstractExpr multiply_with_precision_by_power_of_10(unsigned int t_exponent, unsigned int t_n_digits)

long gcd() const