Multiply

class Multiply(coefficient, filter=<function Multiply.<lambda>>)

Bases: FitnessNormalizer

Multiplies the fitness values by some coefficient.

Examples

Multiplying Fitness Values by a Set of Coefficients

In this example, assume that each fitness value consists of a tuple of numbers, each representing a different property of the molecule, and each contributing to the final fitness value. The properties can be anything, such as energy, number of atoms or diameter.

If your final fitness value depends on the combination of these properties, you will probably first want to scale them with DivideByMean. Once this is done, you may want to multiply each property by some coefficient, which reflects its relative importance to the final fitness value. For example if you multiply the value of one property by 1 and another by 2, the second will contribute twice as much to the final fitness value, assuming that you get the final fitness value by using the Sum normalizer after Multiply.

Giving a concrete example

import stk
import numpy as np

building_block = stk.BuildingBlock(
    smiles='BrCCBr',
    functional_groups=[stk.BromoFactory()],
)

population = (
    stk.MoleculeRecord(
        topology_graph=stk.polymer.Linear(
            building_blocks=(building_block, ),
            repeating_unit='A',
            num_repeating_units=2,
        ),
    ).with_fitness_value(
        fitness_value=(1, 1, 1),
        normalized=False,
    ),
)

normalizer = stk.Multiply((1, 2, 3))
normalized_population = tuple(normalizer.normalize(population))
normalized_record, = normalized_population
assert np.all(np.equal(
    normalized_record.get_fitness_value(),
    (1, 2, 3),
))

Selectively Normalizing Fitness Values

Sometimes, you only want to normalize some members of a population, for example if some do not have an assigned fitness value, because the fitness calculation failed for whatever reason. You can use the filter parameter to exclude records from the normalization

import stk
import numpy as np

building_block = stk.BuildingBlock(
    smiles='BrCCBr',
    functional_groups=[stk.BromoFactory()],
)

population = (
    stk.MoleculeRecord(
        topology_graph=stk.polymer.Linear(
            building_blocks=(building_block, ),
            repeating_unit='A',
            num_repeating_units=2,
        ),
    ).with_fitness_value(
        fitness_value=(1, 1, 1),
        normalized=False,
    ),
    # This will have a fitness value of None.
    stk.MoleculeRecord(
        topology_graph=stk.polymer.Linear(
            building_blocks=(building_block, ),
            repeating_unit='A',
            num_repeating_units=2,
        ),
    ),
)

normalizer = stk.Multiply(
    coefficient=(1, 2, 3),
    # Only normalize values which are not None.
    filter=lambda population, record:
        record.get_fitness_value() is not None,
)

# Calling normalizer.normalize() will return a new
# population holding the molecule records with normalized
# fitness values.
normalized_population = tuple(normalizer.normalize(
    population=population,
))
normalized_record1, normalized_record2 = normalized_population
assert np.all(np.equal(
    normalized_record1.get_fitness_value(),
    (1, 2, 3),
))
assert normalized_record2.get_fitness_value() is None

Methods

normalize(population)

Normalize the fitness values in population.

__init__(coefficient, filter=<function Multiply.<lambda>>)

Initialize a Multiply instance.

Parameters:

• coefficient (float or tuple of float) – The coefficients each fitness value is multiplied by. Can be a single number or multiple numbers, depending on the form of the fitness value.

• filter (callable, optional) – Takes two parameters, first is a tuple of MoleculeRecord instances, and the second is a MoleculeRecord. The callable returns True or False. Only molecules which return True will have fitness values normalized. By default, all molecules will have fitness values normalized. The instance passed to the population argument of normalize() is passed as the first argument, while the second argument will be passed every MoleculeRecord in it, one at a time.

normalize(population)

Normalize the fitness values in population.

Parameters:

population (tuple of MoleculeRecord) – The molecules which need to have their fitness values normalized.

Yields:

MoleculeRecord – A record with a normalized fitness value.