Best selection policy#

New in version 2.11.

#include <pagmo/s_policies/select_best.hpp>

class select_best#

This user-defined selection policy (UDSP) will select the best individuals from a group.

In this context, best means the following:

  • in single-objective unconstrained problems, individuals are ranked according to their fitness function,

  • in single-objective constrained problems, individuals are ranked via sort_population_con(),

  • in multi-objective unconstrained problems, individuals are ranked via sort_population_mo().

See the documentation of select() for more details on the selection algorithm implemented by this UDSP.

Note that this user-defined selection policy currently does not support multi-objective constrained problems.

select_best()#

Default constructor.

The default constructor initialises a policy with an absolute migration rate of 1 (that is, 1 individual will be selected from the input population).

template<typename T>
explicit select_best(T x)#

Constructor from a migration rate.

This constructor participates in overload resolution only if T is a C++ integral or a floating-point type. The input migration rate, x, is used to indicate how many individuals will be selected from an input population by the select() member function.

If x is a floating point value in the \(\left[0,1\right]\) range, then it represents a fractional migration rate. That is, it indicates, the fraction of individuals that will be selected from the input population: a value of 0 means that no individuals will be selected, a value of 1 means that all individuals will be selected.

If x is an integral value, then it represents an absolute migration rate, that is, the exact number of individuals that will be selected from the input population.

Parameters

x – the fractional or absolute migration rate.

Throws

  • std::invalid_argument – if the supplied fractional migration rate is not finite or not in the \(\left[0,1\right]\) range.

  • unspecified – any exception raised by boost::numeric_cast() while trying to convert the input absolute migration rate to pop_size_t.

individuals_group_t select(const individuals_group_t &inds, const vector_double::size_type&, const vector_double::size_type&, const vector_double::size_type &nobj, const vector_double::size_type &nec, const vector_double::size_type &nic, const vector_double &tol) const#

This member function will select individuals from inds.

The selection algorithm determines first how many individuals in inds will be selected. This depends both on the migration rate specified upon construction, and on the size of inds.

After having established the number \(N\) of individuals to be selected from inds, the algorithm then ranks the individuals in inds and selects the top \(N\) individuals. The ranking method depends on the problem’s properties:

  • in single-objective unconstrained problems, the individuals are ranked according to their (scalar) fitnesses,

  • in single-objective constrained problems, the ranking of individuals is done via sort_population_con(),

  • in multi-objective unconstrained problems, the ranking of individuals is done via sort_population_mo().

Note that this user-defined selection policy currently does not support multi-objective constrained problems.

Parameters

  • inds – the input individuals.

  • nobj – the number of objectives of the problem the individuals in inds refer to.

  • nec – the number of equality constraints of the problem the individuals in inds refer to.

  • nic – the number of inequality constraints of the problem the individuals in inds refer to.

  • tol – the vector of constraint tolerances of the problem the individuals in inds refer to.

Returns

the group of top \(N\) individuals from inds.

Throws

  • std::invalid_argument –

    in the following cases:

    • the problem the individuals in inds refer to is multi-objective and constrained,

    • an absolute migration rate larger than the number of input individuals was specified.

  • unspecified – any exception raised by one of the invoked ranking functions or by memory allocation errors in standard containers.

std::string get_name() const#

Get the name of the policy.

Returns

"Select best".

std::string get_extra_info() const#
Returns

Human-readable extra info about this selection policy.