def test_mapwrapper_parallel():
in_arg = np.arange(10.)
out_arg = np.sin(in_arg)
with MapWrapper(2) as p:
out = p(np.sin, in_arg)
assert_equal(list(out), out_arg)
assert_(p._own_pool is True)
assert_(isinstance(p.pool, PWL))
assert_(p._mapfunc is not None)
# the context manager should've closed the internal pool
# check that it has by asking it to calculate again.
with assert_raises(Exception) as excinfo:
p(np.sin, in_arg)
assert_(excinfo.type is ValueError)
# can also set a PoolWrapper up with a map-like callable instance
try:
p = Pool(2)
q = MapWrapper(p.map)
assert_(q._own_pool is False)
q.close()
# closing the PoolWrapper shouldn't close the internal pool
# because it didn't create it
out = p.map(np.sin, in_arg)
assert_equal(list(out), out_arg)
finally:
p.close()
def test_parallel(self):
with MapWrapper(2) as p:
out = p(np.sin, self.input)
assert_equal(list(out), self.output)
assert_(p._own_pool is True)
assert_(isinstance(p.pool, PWL))
assert_(p._mapfunc is not None)
# the context manager should've closed the internal pool
# check that it has by asking it to calculate again.
with assert_raises(Exception) as excinfo:
p(np.sin, self.input)
# on py27 an AssertionError is raised, on >py27 it's a ValueError
err_type = excinfo.type
assert_((err_type is ValueError) or (err_type is AssertionError))
# can also set a PoolWrapper up with a map-like callable instance
try:
p = Pool(2)
q = MapWrapper(p.map)
assert_(q._own_pool is False)
q.close()
# closing the PoolWrapper shouldn't close the internal pool
# because it didn't create it
out = p.map(np.sin, self.input)
assert_equal(list(out), self.output)
finally:
p.close()
def test_parallel(self):
with MapWrapper(2) as p:
out = p(np.sin, self.input)
assert_equal(list(out), self.output)
assert_(p._own_pool is True)
assert_(isinstance(p.pool, PWL))
assert_(p._mapfunc is not None)
# the context manager should've closed the internal pool
# check that it has by asking it to calculate again.
with assert_raises(Exception) as excinfo:
p(np.sin, self.input)
# on py27 an AssertionError is raised, on >py27 it's a ValueError
err_type = excinfo.type
assert_((err_type is ValueError) or (err_type is AssertionError))
# can also set a PoolWrapper up with a map-like callable instance
try:
p = Pool(2)
q = MapWrapper(p.map)
assert_(q._own_pool is False)
q.close()
# closing the PoolWrapper shouldn't close the internal pool
# because it didn't create it
out = p.map(np.sin, self.input)
assert_equal(list(out), self.output)
finally:
p.close()
class EvolutionaryAlgorithmSolver(object):
def __init__(self, func, bounds, args = None, crossover = 'arithmetic',
mutation = 'uniform', generations = 1000, populationSize = 100,
recombinationRate = 0.9, mutationRate = 0.1, seed = None):
self.func = _FunctionWrapper(func, args)
self.bounds = np.array(bounds)
self.seed = check_random_state(seed)
self.crossoverOp = crossover
self.mutationOp = mutation
self.generations = generations
self.popsize = populationSize
self.recombinationrate = recombinationRate
self.mutationrate = mutationRate
self._mapwrapper = MapWrapper(4)
def tournament(self, parents, fitness):
rng = self.seed
idx = np.argsort(rng.uniform(size = (self.popsize, self.popsize)))[:,0:4]
idx_1 = fitness[idx[:,0]] < fitness[idx[:,1]]
idx_2 = fitness[idx[:,2]] < fitness[idx[:,3]]
idx_parent_1 = idx[:,1]
idx_parent_1[idx_1] = idx[idx_1,0]
idx_parent_2 = idx[:,3]
idx_parent_2[idx_2] = idx[idx_2,2]
return (parents[idx_parent_1,:], parents[idx_parent_2,:])
def arithmetic(self, parents):
rng = self.seed
size = np.shape(parents[0])
alpha = rng.uniform(size = size)
mask = rng.choice([False, True], size = (size[0]),
p = [self.recombinationrate, 1-self.recombinationrate])
offspring = np.multiply(alpha, parents[0]) + np.multiply(1-alpha,
parents[1])
offspring[offspring > 1] = 1
offspring[offspring < 0] = 0
offspring[mask] = parents[0][mask]
return offspring
#BLX
def blx(self, parents):
rng = self.seed
size = np.shape(parents[0])
alpha = rng.uniform(size = size)
mask = rng.choice([False, True], size = (size[0]),
p = [self.recombinationrate, 1-self.recombinationrate])
d = np.absolute(parents[0]-parents[1])
alphaD = np.multiply(alpha, d)
q = np.minimum(parents[0],parents[1])-alphaD
r=np.maximum(parents[0],parents[1])+alphaD
offspring= rng.uniform(low=q,high=r)
offspring[offspring > 1] = 1
offspring[offspring < 0] = 0
offspring[mask] = parents[0][mask]
return offspring
#SBX
def sbx(self,parents):
rng = self.seed
size = np.shape(parents[0])
mask = rng.choice([False, True], size = (size[0]),
p = [self.recombinationrate, 1-self.recombinationrate])
u=rng.uniform(size=size)
n=10
b=np.power(2*u,1/n)
#(2*u)**(1/(n+1))
b[u>.5]=np.power(2*(1-u[u>.5]),1/n)
offspring=.5*(parents[0]+parents[1])-.5*np.multiply(b,parents[0]-parents[1])
offspring[offspring > 1] = 1
offspring[offspring < 0] = 0
offspring[mask] = parents[0][mask]
return offspring
def uniform(self, offspring):
rng = self.seed
size=np.shape(offspring)
mutation = rng.uniform(size = size)
mask = rng.choice([True, False], size = size, p = [self.mutationrate, \
1-self.mutationrate])
offspring[mask] = mutation[mask]
return offspring
def boundary(self,offspring):
rng = self.seed
size=np.shape(offspring)
mutation =np.round(rng.uniform(size = size))
mask = rng.choice([True, False], size = size, p = [self.mutationrate, \
1-self.mutationrate])
offspring[mask] = mutation[mask]
return offspring
def __crossover(self, parents):
if self.crossoverOp == 'blx':
return self.blx(parents)
elif self.crossoverOp == 'sbx':
return self.sbx(parents)
elif self.crossoverOp == 'arithmetic':
return self.arithmetic(parents)
else:
raise ValueError("Please select a valid crossover strategy")
def __mutation(self, offspring):
if self.mutationOp == 'uniform':
return self.uniform(offspring)
elif self.mutationOp == 'boundary':
return self.boundary(offspring)
else:
raise ValueError("Please select a valid mutation strategy")
def __reproduce(self, parents):
return self.__mutation(self.__crossover(parents))
def __survivalSelection(self, parents, fparents, offspring, foffspring):
mergedPop = np.vstack((parents, offspring))
mergedFit = np.hstack((fparents, foffspring))
idx = np.argsort(mergedFit)[0:self.popsize]
return mergedPop[idx,:], mergedFit[idx]
def __scaleParameters(self, population):
scaled = np.multiply((self.bounds[:,1] - self.bounds[:,0]), population)
return scaled + self.bounds[:,0]
def solve(self):
rng = self.seed
numVars = np.shape(self.bounds)[0]
# Check the bounds
if not np.all((self.bounds[:,1] - self.bounds[:,0]) > 0):
raise ValueError("Error: lower bound greater than upper bound")
pop = rng.uniform(size=(self.popsize,numVars))
fitness = self.func(self.__scaleParameters(pop))
currentGeneration = 0
while currentGeneration < self.generations + 1:
parents = self.tournament(pop, fitness)
offspring = self.__reproduce(parents)
foffspring = self.func(self.__scaleParameters(offspring))
pop, fitness = self.__survivalSelection(pop, fitness, offspring,
foffspring)
print('The best value in generation '+str(currentGeneration)+ ' is '+str(np.min(fitness)))
currentGeneration += 1
idxBest = np.argmin(fitness)
return (self.__scaleParameters(pop[idxBest,:]), fitness[idxBest])
def __enter__(self):
return self
def __exit__(self, *args):
self._mapwrapper.close()
class DifferentialEvolutionSolver(object):
"""This class implements the differential evolution solver
Parameters
----------
func : callable
The objective function to be minimized. Must be in the form
``f(x, *args)``, where ``x`` is the argument in the form of a 1-D array
and ``args`` is a tuple of any additional fixed parameters needed to
completely specify the function.
bounds : sequence
Bounds for variables. ``(min, max)`` pairs for each element in ``x``,
defining the lower and upper bounds for the optimizing argument of
`func`. It is required to have ``len(bounds) == len(x)``.
``len(bounds)`` is used to determine the number of parameters in ``x``.
args : tuple, optional
Any additional fixed parameters needed to
completely specify the objective function.
strategy : str, optional
The differential evolution strategy to use. Should be one of:
- 'best1bin'
- 'best1exp'
- 'rand1exp'
- 'randtobest1exp'
- 'currenttobest1exp'
- 'best2exp'
- 'rand2exp'
- 'randtobest1bin'
- 'currenttobest1bin'
- 'best2bin'
- 'rand2bin'
- 'rand1bin'
The default is 'best1bin'
maxiter : int, optional
The maximum number of generations over which the entire population is
evolved. The maximum number of function evaluations (with no polishing)
is: ``(maxiter + 1) * popsize * len(x)``
popsize : int, optional
A multiplier for setting the total population size. The population has
``popsize * len(x)`` individuals (unless the initial population is
supplied via the `init` keyword).
tol : float, optional
Relative tolerance for convergence, the solving stops when
``np.std(pop) <= atol + tol * np.abs(np.mean(population_energies))``,
where and `atol` and `tol` are the absolute and relative tolerance
respectively.
mutation : float or tuple(float, float), optional
The mutation constant. In the literature this is also known as
differential weight, being denoted by F.
If specified as a float it should be in the range [0, 2].
If specified as a tuple ``(min, max)`` dithering is employed. Dithering
randomly changes the mutation constant on a generation by generation
basis. The mutation constant for that generation is taken from
U[min, max). Dithering can help speed convergence significantly.
Increasing the mutation constant increases the search radius, but will
slow down convergence.
recombination : float, optional
The recombination constant, should be in the range [0, 1]. In the
literature this is also known as the crossover probability, being
denoted by CR. Increasing this value allows a larger number of mutants
to progress into the next generation, but at the risk of population
stability.
seed : int or `np.random.RandomState`, optional
If `seed` is not specified the `np.random.RandomState` singleton is
used.
If `seed` is an int, a new `np.random.RandomState` instance is used,
seeded with `seed`.
If `seed` is already a `np.random.RandomState` instance, then that
`np.random.RandomState` instance is used.
Specify `seed` for repeatable minimizations.
disp : bool, optional
Display status messages
callback : callable, `callback(xk, convergence=val)`, optional
A function to follow the progress of the minimization. ``xk`` is
the current value of ``x0``. ``val`` represents the fractional
value of the population convergence. When ``val`` is greater than one
the function halts. If callback returns `True`, then the minimization
is halted (any polishing is still carried out).
polish : bool, optional
If True, then `scipy.optimize.minimize` with the `L-BFGS-B` method
is used to polish the best population member at the end. This requires
a few more function evaluations.
maxfun : int, optional
Set the maximum number of function evaluations. However, it probably
makes more sense to set `maxiter` instead.
init : str or array-like, optional
Specify which type of population initialization is performed. Should be
one of:
- 'latinhypercube'
- 'random'
- array specifying the initial population. The array should have
shape ``(M, len(x))``, where len(x) is the number of parameters.
`init` is clipped to `bounds` before use.
The default is 'latinhypercube'. Latin Hypercube sampling tries to
maximize coverage of the available parameter space. 'random'
initializes the population randomly - this has the drawback that
clustering can occur, preventing the whole of parameter space being
covered. Use of an array to specify a population could be used, for
example, to create a tight bunch of initial guesses in an location
where the solution is known to exist, thereby reducing time for
convergence.
atol : float, optional
Absolute tolerance for convergence, the solving stops when
``np.std(pop) <= atol + tol * np.abs(np.mean(population_energies))``,
where and `atol` and `tol` are the absolute and relative tolerance
respectively.
updating : {'immediate', 'deferred'}, optional
If `immediate` the best solution vector is continuously updated within
a single generation. This can lead to faster convergence as trial
vectors can take advantage of continuous improvements in the best
solution.
With `deferred` the best solution vector is updated once per
generation. Only `deferred` is compatible with parallelization, and the
`workers` keyword can over-ride this option.
workers : int or map-like callable, optional
If `workers` is an int the population is subdivided into `workers`
sections and evaluated in parallel (uses `multiprocessing.Pool`).
Supply `-1` to use all cores available to the Process.
Alternatively supply a map-like callable, such as
`multiprocessing.Pool.map` for evaluating the population in parallel.
This evaluation is carried out as ``workers(func, iterable)``.
This option will override the `updating` keyword to
`updating='deferred'` if `workers != 1`.
Requires that `func` be pickleable.
"""
# Dispatch of mutation strategy method (binomial or exponential).
_binomial = {'best1bin': '_best1',
'randtobest1bin': '_randtobest1',
'currenttobest1bin': '_currenttobest1',
'best2bin': '_best2',
'rand2bin': '_rand2',
'rand1bin': '_rand1'}
_exponential = {'best1exp': '_best1',
'rand1exp': '_rand1',
'randtobest1exp': '_randtobest1',
'currenttobest1exp': '_currenttobest1',
'best2exp': '_best2',
'rand2exp': '_rand2'}
__init_error_msg = ("The population initialization method must be one of "
"'latinhypercube' or 'random', or an array of shape "
"(M, N) where N is the number of parameters and M>5")
def __init__(self, func, bounds, args=(),
strategy='best1bin', maxiter=1000, popsize=15,
tol=0.01, mutation=(0.5, 1), recombination=0.7, seed=None,
maxfun=np.inf, callback=None, disp=False, polish=True,
init='latinhypercube', atol=0, updating='immediate',
workers=1):
if strategy in self._binomial:
self.mutation_func = getattr(self, self._binomial[strategy])
elif strategy in self._exponential:
self.mutation_func = getattr(self, self._exponential[strategy])
else:
raise ValueError("Please select a valid mutation strategy")
self.strategy = strategy
self.callback = callback
self.polish = polish
# set the updating / parallelisation options
if updating in ['immediate', 'deferred']:
self._updating = updating
# want to use parallelisation, but updating is immediate
if workers != 1 and updating == 'immediate':
warnings.warn("differential_evolution: the 'workers' keyword has"
" overridden updating='immediate' to"
" updating='deferred'", UserWarning)
self._updating = 'deferred'
# an object with a map method.
self._mapwrapper = MapWrapper(workers)
# relative and absolute tolerances for convergence
self.tol, self.atol = tol, atol
# Mutation constant should be in [0, 2). If specified as a sequence
# then dithering is performed.
self.scale = mutation
if (not np.all(np.isfinite(mutation)) or
np.any(np.array(mutation) >= 2) or
np.any(np.array(mutation) < 0)):
raise ValueError('The mutation constant must be a float in '
'U[0, 2), or specified as a tuple(min, max)'
' where min < max and min, max are in U[0, 2).')
self.dither = None
if hasattr(mutation, '__iter__') and len(mutation) > 1:
self.dither = [mutation[0], mutation[1]]
self.dither.sort()
self.cross_over_probability = recombination
# we create a wrapped function to allow the use of map (and Pool.map
# in the future)
self.func = _FunctionWrapper(func, args)
self.args = args
# convert tuple of lower and upper bounds to limits
# [(low_0, high_0), ..., (low_n, high_n]
# -> [[low_0, ..., low_n], [high_0, ..., high_n]]
self.limits = np.array(bounds, dtype='float').T
if (np.size(self.limits, 0) != 2 or not
np.all(np.isfinite(self.limits))):
raise ValueError('bounds should be a sequence containing '
'real valued (min, max) pairs for each value'
' in x')
if maxiter is None: # the default used to be None
maxiter = 1000
self.maxiter = maxiter
if maxfun is None: # the default used to be None
maxfun = np.inf
self.maxfun = maxfun
# population is scaled to between [0, 1].
# We have to scale between parameter <-> population
# save these arguments for _scale_parameter and
# _unscale_parameter. This is an optimization
self.__scale_arg1 = 0.5 * (self.limits[0] + self.limits[1])
self.__scale_arg2 = np.fabs(self.limits[0] - self.limits[1])
self.parameter_count = np.size(self.limits, 1)
self.random_number_generator = check_random_state(seed)
# default population initialization is a latin hypercube design, but
# there are other population initializations possible.
# the minimum is 5 because 'best2bin' requires a population that's at
# least 5 long
self.num_population_members = max(5, popsize * self.parameter_count)
self.population_shape = (self.num_population_members,
self.parameter_count)
self._nfev = 0
if isinstance(init, string_types):
if init == 'latinhypercube':
self.init_population_lhs()
elif init == 'random':
self.init_population_random()
else:
raise ValueError(self.__init_error_msg)
else:
self.init_population_array(init)
self.disp = disp
def init_population_lhs(self):
"""
Initializes the population with Latin Hypercube Sampling.
Latin Hypercube Sampling ensures that each parameter is uniformly
sampled over its range.
"""
rng = self.random_number_generator
# Each parameter range needs to be sampled uniformly. The scaled
# parameter range ([0, 1)) needs to be split into
# `self.num_population_members` segments, each of which has the following
# size:
segsize = 1.0 / self.num_population_members
# Within each segment we sample from a uniform random distribution.
# We need to do this sampling for each parameter.
samples = (segsize * rng.random_sample(self.population_shape)
# Offset each segment to cover the entire parameter range [0, 1)
+ np.linspace(0., 1., self.num_population_members,
endpoint=False)[:, np.newaxis])
# Create an array for population of candidate solutions.
self.population = np.zeros_like(samples)
# Initialize population of candidate solutions by permutation of the
# random samples.
for j in range(self.parameter_count):
order = rng.permutation(range(self.num_population_members))
self.population[:, j] = samples[order, j]
# reset population energies
self.population_energies = np.full(self.num_population_members,
np.inf)
# reset number of function evaluations counter
self._nfev = 0
def init_population_random(self):
"""
Initialises the population at random. This type of initialization
can possess clustering, Latin Hypercube sampling is generally better.
"""
rng = self.random_number_generator
self.population = rng.random_sample(self.population_shape)
# reset population energies
self.population_energies = np.full(self.num_population_members,
np.inf)
# reset number of function evaluations counter
self._nfev = 0
def init_population_array(self, init):
"""
Initialises the population with a user specified population.
Parameters
----------
init : np.ndarray
Array specifying subset of the initial population. The array should
have shape (M, len(x)), where len(x) is the number of parameters.
The population is clipped to the lower and upper bounds.
"""
# make sure you're using a float array
popn = np.asfarray(init)
if (np.size(popn, 0) < 5 or
popn.shape[1] != self.parameter_count or
len(popn.shape) != 2):
raise ValueError("The population supplied needs to have shape"
" (M, len(x)), where M > 4.")
# scale values and clip to bounds, assigning to population
self.population = np.clip(self._unscale_parameters(popn), 0, 1)
self.num_population_members = np.size(self.population, 0)
self.population_shape = (self.num_population_members,
self.parameter_count)
# reset population energies
self.population_energies = (np.ones(self.num_population_members) *
np.inf)
# reset number of function evaluations counter
self._nfev = 0
@property
def x(self):
"""
The best solution from the solver
"""
return self._scale_parameters(self.population[0])
@property
def convergence(self):
"""
The standard deviation of the population energies divided by their
mean.
"""
if np.any(np.isinf(self.population_energies)):
return np.inf
return (np.std(self.population_energies) /
np.abs(np.mean(self.population_energies) + _MACHEPS))
def converged(self):
"""
Return True if the solver has converged.
"""
return (np.std(self.population_energies) <=
self.atol +
self.tol * np.abs(np.mean(self.population_energies)))
def solve(self):
"""
Runs the DifferentialEvolutionSolver.
Returns
-------
res : OptimizeResult
The optimization result represented as a ``OptimizeResult`` object.
Important attributes are: ``x`` the solution array, ``success`` a
Boolean flag indicating if the optimizer exited successfully and
``message`` which describes the cause of the termination. See
`OptimizeResult` for a description of other attributes. If `polish`
was employed, and a lower minimum was obtained by the polishing,
then OptimizeResult also contains the ``jac`` attribute.
"""
nit, warning_flag = 0, False
status_message = _status_message['success']
# The population may have just been initialized (all entries are
# np.inf). If it has you have to calculate the initial energies.
# Although this is also done in the evolve generator it's possible
# that someone can set maxiter=0, at which point we still want the
# initial energies to be calculated (the following loop isn't run).
if np.all(np.isinf(self.population_energies)):
self.population_energies[:] = self._calculate_population_energies(
self.population)
self._promote_lowest_energy()
# do the optimisation.
for nit in xrange(1, self.maxiter + 1):
# evolve the population by a generation
try:
next(self)
except StopIteration:
warning_flag = True
if self._nfev > self.maxfun:
status_message = _status_message['maxfev']
elif self._nfev == self.maxfun:
status_message = ('Maximum number of function evaluations'
' has been reached.')
break
if self.disp:
print("differential_evolution step %d: f(x)= %g"
% (nit,
self.population_energies[0]))
# should the solver terminate?
convergence = self.convergence
if (self.callback and
self.callback(self._scale_parameters(self.population[0]),
convergence=self.tol / convergence) is True):
warning_flag = True
status_message = ('callback function requested stop early '
'by returning True')
break
if np.any(np.isinf(self.population_energies)):
intol = False
else:
intol = (np.std(self.population_energies) <=
self.atol +
self.tol * np.abs(np.mean(self.population_energies)))
if warning_flag or intol:
break
else:
status_message = _status_message['maxiter']
warning_flag = True
DE_result = OptimizeResult(
x=self.x,
fun=self.population_energies[0],
nfev=self._nfev,
nit=nit,
message=status_message,
success=(warning_flag is not True))
if self.polish:
result = minimize(self.func,
np.copy(DE_result.x),
method='L-BFGS-B',
bounds=self.limits.T)
self._nfev += result.nfev
DE_result.nfev = self._nfev
if result.fun < DE_result.fun:
DE_result.fun = result.fun
DE_result.x = result.x
DE_result.jac = result.jac
# to keep internal state consistent
self.population_energies[0] = result.fun
self.population[0] = self._unscale_parameters(result.x)
return DE_result
def _calculate_population_energies(self, population):
"""
Calculate the energies of all the population members at the same time.
Parameters
----------
population : ndarray
An array of parameter vectors normalised to [0, 1] using lower
and upper limits. Has shape ``(np.size(population, 0), len(x))``.
Returns
-------
energies : ndarray
An array of energies corresponding to each population member. If
maxfun will be exceeded during this call, then the number of
function evaluations will be reduced and energies will be
right-padded with np.inf. Has shape ``(np.size(population, 0),)``
"""
num_members = np.size(population, 0)
nfevs = min(num_members,
self.maxfun - num_members)
energies = np.full(num_members, np.inf)
parameters_pop = self._scale_parameters(population)
try:
calc_energies = list(self._mapwrapper(self.func,
parameters_pop[0:nfevs]))
energies[0:nfevs] = calc_energies
except (TypeError, ValueError):
# wrong number of arguments for _mapwrapper
# or wrong length returned from the mapper
raise RuntimeError("The map-like callable must be of the"
" form f(func, iterable), returning a sequence"
" of numbers the same length as 'iterable'")
self._nfev += nfevs
return energies
def _promote_lowest_energy(self):
# promotes the lowest energy to the first entry in the population
l = np.argmin(self.population_energies)
# put the lowest energy into the best solution position.
self.population_energies[[0, l]] = self.population_energies[[l, 0]]
self.population[[0, l], :] = self.population[[l, 0], :]
def __iter__(self):
return self
def __enter__(self):
return self
def __exit__(self, *args):
# to make sure resources are closed down
self._mapwrapper.close()
def __del__(self):
# to make sure resources are closed down
self._mapwrapper.close()
def __next__(self):
"""
Evolve the population by a single generation
Returns
-------
x : ndarray
The best solution from the solver.
fun : float
Value of objective function obtained from the best solution.
"""
# the population may have just been initialized (all entries are
# np.inf). If it has you have to calculate the initial energies
if np.all(np.isinf(self.population_energies)):
self.population_energies[:] = self._calculate_population_energies(
self.population)
self._promote_lowest_energy()
if self.dither is not None:
self.scale = (self.random_number_generator.rand()
* (self.dither[1] - self.dither[0]) + self.dither[0])
if self._updating == 'immediate':
# update best solution immediately
for candidate in range(self.num_population_members):
if self._nfev > self.maxfun:
raise StopIteration
# create a trial solution
trial = self._mutate(candidate)
# ensuring that it's in the range [0, 1)
self._ensure_constraint(trial)
# scale from [0, 1) to the actual parameter value
parameters = self._scale_parameters(trial)
# determine the energy of the objective function
energy = self.func(parameters)
self._nfev += 1
# if the energy of the trial candidate is lower than the
# original population member then replace it
if energy < self.population_energies[candidate]:
self.population[candidate] = trial
self.population_energies[candidate] = energy
# if the trial candidate also has a lower energy than the
# best solution then promote it to the best solution.
if energy < self.population_energies[0]:
self._promote_lowest_energy()
elif self._updating == 'deferred':
# update best solution once per generation
if self._nfev >= self.maxfun:
raise StopIteration
# 'deferred' approach, vectorised form.
# create trial solutions
trial_pop = np.array(
[self._mutate(i) for i in range(self.num_population_members)])
# enforce bounds
self._ensure_constraint(trial_pop)
# determine the energies of the objective function
trial_energies = self._calculate_population_energies(trial_pop)
# which solutions are improved?
loc = trial_energies < self.population_energies
self.population = np.where(loc[:, np.newaxis],
trial_pop,
self.population)
self.population_energies = np.where(loc,
trial_energies,
self.population_energies)
# make sure the best solution is updated if updating='deferred'.
# put the lowest energy into the best solution position.
self._promote_lowest_energy()
return self.x, self.population_energies[0]
next = __next__
def _scale_parameters(self, trial):
"""Scale from a number between 0 and 1 to parameters."""
return self.__scale_arg1 + (trial - 0.5) * self.__scale_arg2
def _unscale_parameters(self, parameters):
"""Scale from parameters to a number between 0 and 1."""
return (parameters - self.__scale_arg1) / self.__scale_arg2 + 0.5
def _ensure_constraint(self, trial):
"""Make sure the parameters lie between the limits."""
mask = np.where((trial > 1) | (trial < 0))
trial[mask] = self.random_number_generator.rand(mask[0].size)
def _mutate(self, candidate):
"""Create a trial vector based on a mutation strategy."""
trial = np.copy(self.population[candidate])
rng = self.random_number_generator
fill_point = rng.randint(0, self.parameter_count)
if self.strategy in ['currenttobest1exp', 'currenttobest1bin']:
bprime = self.mutation_func(candidate,
self._select_samples(candidate, 5))
else:
bprime = self.mutation_func(self._select_samples(candidate, 5))
if self.strategy in self._binomial:
crossovers = rng.rand(self.parameter_count)
crossovers = crossovers < self.cross_over_probability
# the last one is always from the bprime vector for binomial
# If you fill in modulo with a loop you have to set the last one to
# true. If you don't use a loop then you can have any random entry
# be True.
crossovers[fill_point] = True
trial = np.where(crossovers, bprime, trial)
return trial
elif self.strategy in self._exponential:
i = 0
while (i < self.parameter_count and
rng.rand() < self.cross_over_probability):
trial[fill_point] = bprime[fill_point]
fill_point = (fill_point + 1) % self.parameter_count
i += 1
return trial
def _best1(self, samples):
"""best1bin, best1exp"""
r0, r1 = samples[:2]
return (self.population[0] + self.scale *
(self.population[r0] - self.population[r1]))
def _rand1(self, samples):
"""rand1bin, rand1exp"""
r0, r1, r2 = samples[:3]
return (self.population[r0] + self.scale *
(self.population[r1] - self.population[r2]))
def _randtobest1(self, samples):
"""randtobest1bin, randtobest1exp"""
r0, r1, r2 = samples[:3]
bprime = np.copy(self.population[r0])
bprime += self.scale * (self.population[0] - bprime)
bprime += self.scale * (self.population[r1] -
self.population[r2])
return bprime
def _currenttobest1(self, candidate, samples):
"""currenttobest1bin, currenttobest1exp"""
r0, r1 = samples[:2]
bprime = (self.population[candidate] + self.scale *
(self.population[0] - self.population[candidate] +
self.population[r0] - self.population[r1]))
return bprime
def _best2(self, samples):
"""best2bin, best2exp"""
r0, r1, r2, r3 = samples[:4]
bprime = (self.population[0] + self.scale *
(self.population[r0] + self.population[r1] -
self.population[r2] - self.population[r3]))
return bprime
def _rand2(self, samples):
"""rand2bin, rand2exp"""
r0, r1, r2, r3, r4 = samples
bprime = (self.population[r0] + self.scale *
(self.population[r1] + self.population[r2] -
self.population[r3] - self.population[r4]))
return bprime
def _select_samples(self, candidate, number_samples):
"""
obtain random integers from range(self.num_population_members),
without replacement. You can't have the original candidate either.
"""
idxs = list(range(self.num_population_members))
idxs.remove(candidate)
self.random_number_generator.shuffle(idxs)
idxs = idxs[:number_samples]
return idxs
class DifferentialEvolutionSolver(object):
"""This class implements the differential evolution solver
Parameters
----------
func : callable
The objective function to be minimized. Must be in the form
``f(x, *args)``, where ``x`` is the argument in the form of a 1-D array
and ``args`` is a tuple of any additional fixed parameters needed to
completely specify the function.
bounds : sequence
Bounds for variables. ``(min, max)`` pairs for each element in ``x``,
defining the lower and upper bounds for the optimizing argument of
`func`. It is required to have ``len(bounds) == len(x)``.
``len(bounds)`` is used to determine the number of parameters in ``x``.
args : tuple, optional
Any additional fixed parameters needed to
completely specify the objective function.
strategy : str, optional
The differential evolution strategy to use. Should be one of:
- 'best1bin'
- 'best1exp'
- 'rand1exp'
- 'randtobest1exp'
- 'currenttobest1exp'
- 'best2exp'
- 'rand2exp'
- 'randtobest1bin'
- 'currenttobest1bin'
- 'best2bin'
- 'rand2bin'
- 'rand1bin'
The default is 'best1bin'
maxiter : int, optional
The maximum number of generations over which the entire population is
evolved. The maximum number of function evaluations (with no polishing)
is: ``(maxiter + 1) * popsize * len(x)``
popsize : int, optional
A multiplier for setting the total population size. The population has
``popsize * len(x)`` individuals (unless the initial population is
supplied via the `init` keyword).
tol : float, optional
Relative tolerance for convergence, the solving stops when
``np.std(pop) <= atol + tol * np.abs(np.mean(population_energies))``,
where and `atol` and `tol` are the absolute and relative tolerance
respectively.
mutation : float or tuple(float, float), optional
The mutation constant. In the literature this is also known as
differential weight, being denoted by F.
If specified as a float it should be in the range [0, 2].
If specified as a tuple ``(min, max)`` dithering is employed. Dithering
randomly changes the mutation constant on a generation by generation
basis. The mutation constant for that generation is taken from
U[min, max). Dithering can help speed convergence significantly.
Increasing the mutation constant increases the search radius, but will
slow down convergence.
recombination : float, optional
The recombination constant, should be in the range [0, 1]. In the
literature this is also known as the crossover probability, being
denoted by CR. Increasing this value allows a larger number of mutants
to progress into the next generation, but at the risk of population
stability.
seed : int or `np.random.RandomState`, optional
If `seed` is not specified the `np.random.RandomState` singleton is
used.
If `seed` is an int, a new `np.random.RandomState` instance is used,
seeded with `seed`.
If `seed` is already a `np.random.RandomState` instance, then that
`np.random.RandomState` instance is used.
Specify `seed` for repeatable minimizations.
disp : bool, optional
Display status messages
callback : callable, `callback(xk, convergence=val)`, optional
A function to follow the progress of the minimization. ``xk`` is
the current value of ``x0``. ``val`` represents the fractional
value of the population convergence. When ``val`` is greater than one
the function halts. If callback returns `True`, then the minimization
is halted (any polishing is still carried out).
polish : bool, optional
If True, then `scipy.optimize.minimize` with the `L-BFGS-B` method
is used to polish the best population member at the end. This requires
a few more function evaluations.
maxfun : int, optional
Set the maximum number of function evaluations. However, it probably
makes more sense to set `maxiter` instead.
init : str or array-like, optional
Specify which type of population initialization is performed. Should be
one of:
- 'latinhypercube'
- 'random'
- array specifying the initial population. The array should have
shape ``(M, len(x))``, where len(x) is the number of parameters.
`init` is clipped to `bounds` before use.
The default is 'latinhypercube'. Latin Hypercube sampling tries to
maximize coverage of the available parameter space. 'random'
initializes the population randomly - this has the drawback that
clustering can occur, preventing the whole of parameter space being
covered. Use of an array to specify a population could be used, for
example, to create a tight bunch of initial guesses in an location
where the solution is known to exist, thereby reducing time for
convergence.
atol : float, optional
Absolute tolerance for convergence, the solving stops when
``np.std(pop) <= atol + tol * np.abs(np.mean(population_energies))``,
where and `atol` and `tol` are the absolute and relative tolerance
respectively.
updating : {'immediate', 'deferred'}, optional
If `immediate` the best solution vector is continuously updated within
a single generation. This can lead to faster convergence as trial
vectors can take advantage of continuous improvements in the best
solution.
With `deferred` the best solution vector is updated once per
generation. Only `deferred` is compatible with parallelization, and the
`workers` keyword can over-ride this option.
workers : int or map-like callable, optional
If `workers` is an int the population is subdivided into `workers`
sections and evaluated in parallel (uses `multiprocessing.Pool`).
Supply `-1` to use all cores available to the Process.
Alternatively supply a map-like callable, such as
`multiprocessing.Pool.map` for evaluating the population in parallel.
This evaluation is carried out as ``workers(func, iterable)``.
This option will override the `updating` keyword to
`updating='deferred'` if `workers != 1`.
Requires that `func` be pickleable.
"""
# Dispatch of mutation strategy method (binomial or exponential).
_binomial = {
'best1bin': '_best1',
'randtobest1bin': '_randtobest1',
'currenttobest1bin': '_currenttobest1',
'best2bin': '_best2',
'rand2bin': '_rand2',
'rand1bin': '_rand1'
}
_exponential = {
'best1exp': '_best1',
'rand1exp': '_rand1',
'randtobest1exp': '_randtobest1',
'currenttobest1exp': '_currenttobest1',
'best2exp': '_best2',
'rand2exp': '_rand2'
}
__init_error_msg = ("The population initialization method must be one of "
"'latinhypercube' or 'random', or an array of shape "
"(M, N) where N is the number of parameters and M>5")
def __init__(self,
func,
bounds,
args=(),
strategy='best1bin',
maxiter=1000,
popsize=15,
tol=0.01,
mutation=(0.5, 1),
recombination=0.7,
seed=None,
maxfun=np.inf,
callback=None,
disp=False,
polish=True,
init='latinhypercube',
atol=0,
updating='immediate',
workers=1):
if strategy in self._binomial:
self.mutation_func = getattr(self, self._binomial[strategy])
elif strategy in self._exponential:
self.mutation_func = getattr(self, self._exponential[strategy])
else:
raise ValueError("Please select a valid mutation strategy")
self.strategy = strategy
self.callback = callback
self.polish = polish
# set the updating / parallelisation options
if updating in ['immediate', 'deferred']:
self._updating = updating
# want to use parallelisation, but updating is immediate
if workers != 1 and updating == 'immediate':
warnings.warn(
"differential_evolution: the 'workers' keyword has"
" overridden updating='immediate' to"
" updating='deferred'", UserWarning)
self._updating = 'deferred'
# an object with a map method.
self._mapwrapper = MapWrapper(workers)
# relative and absolute tolerances for convergence
self.tol, self.atol = tol, atol
# Mutation constant should be in [0, 2). If specified as a sequence
# then dithering is performed.
self.scale = mutation
if (not np.all(np.isfinite(mutation))
or np.any(np.array(mutation) >= 2)
or np.any(np.array(mutation) < 0)):
raise ValueError('The mutation constant must be a float in '
'U[0, 2), or specified as a tuple(min, max)'
' where min < max and min, max are in U[0, 2).')
self.dither = None
if hasattr(mutation, '__iter__') and len(mutation) > 1:
self.dither = [mutation[0], mutation[1]]
self.dither.sort()
self.cross_over_probability = recombination
# we create a wrapped function to allow the use of map (and Pool.map
# in the future)
self.func = _FunctionWrapper(func, args)
self.args = args
# convert tuple of lower and upper bounds to limits
# [(low_0, high_0), ..., (low_n, high_n]
# -> [[low_0, ..., low_n], [high_0, ..., high_n]]
self.limits = np.array(bounds, dtype='float').T
if (np.size(self.limits, 0) != 2
or not np.all(np.isfinite(self.limits))):
raise ValueError('bounds should be a sequence containing '
'real valued (min, max) pairs for each value'
' in x')
if maxiter is None: # the default used to be None
maxiter = 1000
self.maxiter = maxiter
if maxfun is None: # the default used to be None
maxfun = np.inf
self.maxfun = maxfun
# population is scaled to between [0, 1].
# We have to scale between parameter <-> population
# save these arguments for _scale_parameter and
# _unscale_parameter. This is an optimization
self.__scale_arg1 = 0.5 * (self.limits[0] + self.limits[1])
self.__scale_arg2 = np.fabs(self.limits[0] - self.limits[1])
self.parameter_count = np.size(self.limits, 1)
self.random_number_generator = check_random_state(seed)
# default population initialization is a latin hypercube design, but
# there are other population initializations possible.
# the minimum is 5 because 'best2bin' requires a population that's at
# least 5 long
self.num_population_members = max(5, popsize * self.parameter_count)
self.population_shape = (self.num_population_members,
self.parameter_count)
self._nfev = 0
if isinstance(init, string_types):
if init == 'latinhypercube':
self.init_population_lhs()
elif init == 'random':
self.init_population_random()
else:
raise ValueError(self.__init_error_msg)
else:
self.init_population_array(init)
self.disp = disp
def init_population_lhs(self):
"""
Initializes the population with Latin Hypercube Sampling.
Latin Hypercube Sampling ensures that each parameter is uniformly
sampled over its range.
"""
rng = self.random_number_generator
# Each parameter range needs to be sampled uniformly. The scaled
# parameter range ([0, 1)) needs to be split into
# `self.num_population_members` segments, each of which has the following
# size:
segsize = 1.0 / self.num_population_members
# Within each segment we sample from a uniform random distribution.
# We need to do this sampling for each parameter.
samples = (
segsize * rng.random_sample(self.population_shape)
# Offset each segment to cover the entire parameter range [0, 1)
+ np.linspace(0., 1., self.num_population_members,
endpoint=False)[:, np.newaxis])
# Create an array for population of candidate solutions.
self.population = np.zeros_like(samples)
# Initialize population of candidate solutions by permutation of the
# random samples.
for j in range(self.parameter_count):
order = rng.permutation(range(self.num_population_members))
self.population[:, j] = samples[order, j]
# reset population energies
self.population_energies = np.full(self.num_population_members, np.inf)
# reset number of function evaluations counter
self._nfev = 0
def init_population_random(self):
"""
Initialises the population at random. This type of initialization
can possess clustering, Latin Hypercube sampling is generally better.
"""
rng = self.random_number_generator
self.population = rng.random_sample(self.population_shape)
# reset population energies
self.population_energies = np.full(self.num_population_members, np.inf)
# reset number of function evaluations counter
self._nfev = 0
def init_population_array(self, init):
"""
Initialises the population with a user specified population.
Parameters
----------
init : np.ndarray
Array specifying subset of the initial population. The array should
have shape (M, len(x)), where len(x) is the number of parameters.
The population is clipped to the lower and upper bounds.
"""
# make sure you're using a float array
popn = np.asfarray(init)
if (np.size(popn, 0) < 5 or popn.shape[1] != self.parameter_count
or len(popn.shape) != 2):
raise ValueError("The population supplied needs to have shape"
" (M, len(x)), where M > 4.")
# scale values and clip to bounds, assigning to population
self.population = np.clip(self._unscale_parameters(popn), 0, 1)
self.num_population_members = np.size(self.population, 0)
self.population_shape = (self.num_population_members,
self.parameter_count)
# reset population energies
self.population_energies = (np.ones(self.num_population_members) *
np.inf)
# reset number of function evaluations counter
self._nfev = 0
@property
def x(self):
"""
The best solution from the solver
"""
return self._scale_parameters(self.population[0])
@property
def convergence(self):
"""
The standard deviation of the population energies divided by their
mean.
"""
if np.any(np.isinf(self.population_energies)):
return np.inf
return (np.std(self.population_energies) /
np.abs(np.mean(self.population_energies) + _MACHEPS))
def converged(self):
"""
Return True if the solver has converged.
"""
return (np.std(self.population_energies) <= self.atol +
self.tol * np.abs(np.mean(self.population_energies)))
def solve(self):
"""
Runs the DifferentialEvolutionSolver.
Returns
-------
res : OptimizeResult
The optimization result represented as a ``OptimizeResult`` object.
Important attributes are: ``x`` the solution array, ``success`` a
Boolean flag indicating if the optimizer exited successfully and
``message`` which describes the cause of the termination. See
`OptimizeResult` for a description of other attributes. If `polish`
was employed, and a lower minimum was obtained by the polishing,
then OptimizeResult also contains the ``jac`` attribute.
"""
nit, warning_flag = 0, False
status_message = _status_message['success']
# The population may have just been initialized (all entries are
# np.inf). If it has you have to calculate the initial energies.
# Although this is also done in the evolve generator it's possible
# that someone can set maxiter=0, at which point we still want the
# initial energies to be calculated (the following loop isn't run).
if np.all(np.isinf(self.population_energies)):
self.population_energies[:] = self._calculate_population_energies(
self.population)
self._promote_lowest_energy()
# do the optimisation.
for nit in xrange(1, self.maxiter + 1):
# evolve the population by a generation
try:
next(self)
except StopIteration:
warning_flag = True
if self._nfev > self.maxfun:
status_message = _status_message['maxfev']
elif self._nfev == self.maxfun:
status_message = ('Maximum number of function evaluations'
' has been reached.')
break
if self.disp:
print("differential_evolution step %d: f(x)= %g" %
(nit, self.population_energies[0]))
# should the solver terminate?
convergence = self.convergence
if (self.callback and
self.callback(self._scale_parameters(self.population[0]),
convergence=self.tol / convergence) is True):
warning_flag = True
status_message = ('callback function requested stop early '
'by returning True')
break
if np.any(np.isinf(self.population_energies)):
intol = False
else:
intol = (np.std(self.population_energies) <= self.atol +
self.tol * np.abs(np.mean(self.population_energies)))
if warning_flag or intol:
break
else:
status_message = _status_message['maxiter']
warning_flag = True
DE_result = OptimizeResult(x=self.x,
fun=self.population_energies[0],
nfev=self._nfev,
nit=nit,
message=status_message,
success=(warning_flag is not True))
if self.polish:
result = minimize(self.func,
np.copy(DE_result.x),
method='L-BFGS-B',
bounds=self.limits.T)
self._nfev += result.nfev
DE_result.nfev = self._nfev
if result.fun < DE_result.fun:
DE_result.fun = result.fun
DE_result.x = result.x
DE_result.jac = result.jac
# to keep internal state consistent
self.population_energies[0] = result.fun
self.population[0] = self._unscale_parameters(result.x)
return DE_result
def _calculate_population_energies(self, population):
"""
Calculate the energies of all the population members at the same time.
Parameters
----------
population : ndarray
An array of parameter vectors normalised to [0, 1] using lower
and upper limits. Has shape ``(np.size(population, 0), len(x))``.
Returns
-------
energies : ndarray
An array of energies corresponding to each population member. If
maxfun will be exceeded during this call, then the number of
function evaluations will be reduced and energies will be
right-padded with np.inf. Has shape ``(np.size(population, 0),)``
"""
num_members = np.size(population, 0)
nfevs = min(num_members, self.maxfun - num_members)
energies = np.full(num_members, np.inf)
parameters_pop = self._scale_parameters(population)
try:
calc_energies = list(
self._mapwrapper(self.func, parameters_pop[0:nfevs]))
energies[0:nfevs] = calc_energies
except (TypeError, ValueError):
# wrong number of arguments for _mapwrapper
# or wrong length returned from the mapper
raise RuntimeError("The map-like callable must be of the"
" form f(func, iterable), returning a sequence"
" of numbers the same length as 'iterable'")
self._nfev += nfevs
return energies
def _promote_lowest_energy(self):
# promotes the lowest energy to the first entry in the population
l = np.argmin(self.population_energies)
# put the lowest energy into the best solution position.
self.population_energies[[0, l]] = self.population_energies[[l, 0]]
self.population[[0, l], :] = self.population[[l, 0], :]
def __iter__(self):
return self
def __enter__(self):
return self
def __exit__(self, *args):
# to make sure resources are closed down
self._mapwrapper.close()
def __del__(self):
# to make sure resources are closed down
self._mapwrapper.close()
def __next__(self):
"""
Evolve the population by a single generation
Returns
-------
x : ndarray
The best solution from the solver.
fun : float
Value of objective function obtained from the best solution.
"""
# the population may have just been initialized (all entries are
# np.inf). If it has you have to calculate the initial energies
if np.all(np.isinf(self.population_energies)):
self.population_energies[:] = self._calculate_population_energies(
self.population)
self._promote_lowest_energy()
if self.dither is not None:
self.scale = (self.random_number_generator.rand() *
(self.dither[1] - self.dither[0]) + self.dither[0])
if self._updating == 'immediate':
# update best solution immediately
for candidate in range(self.num_population_members):
if self._nfev > self.maxfun:
raise StopIteration
# create a trial solution
trial = self._mutate(candidate)
# ensuring that it's in the range [0, 1)
self._ensure_constraint(trial)
# scale from [0, 1) to the actual parameter value
parameters = self._scale_parameters(trial)
# determine the energy of the objective function
energy = self.func(parameters)
self._nfev += 1
# if the energy of the trial candidate is lower than the
# original population member then replace it
if energy < self.population_energies[candidate]:
self.population[candidate] = trial
self.population_energies[candidate] = energy
# if the trial candidate also has a lower energy than the
# best solution then promote it to the best solution.
if energy < self.population_energies[0]:
self._promote_lowest_energy()
elif self._updating == 'deferred':
# update best solution once per generation
if self._nfev >= self.maxfun:
raise StopIteration
# 'deferred' approach, vectorised form.
# create trial solutions
trial_pop = np.array(
[self._mutate(i) for i in range(self.num_population_members)])
# enforce bounds
self._ensure_constraint(trial_pop)
# determine the energies of the objective function
trial_energies = self._calculate_population_energies(trial_pop)
# which solutions are improved?
loc = trial_energies < self.population_energies
self.population = np.where(loc[:, np.newaxis], trial_pop,
self.population)
self.population_energies = np.where(loc, trial_energies,
self.population_energies)
# make sure the best solution is updated if updating='deferred'.
# put the lowest energy into the best solution position.
self._promote_lowest_energy()
return self.x, self.population_energies[0]
next = __next__
def _scale_parameters(self, trial):
"""Scale from a number between 0 and 1 to parameters."""
return self.__scale_arg1 + (trial - 0.5) * self.__scale_arg2
def _unscale_parameters(self, parameters):
"""Scale from parameters to a number between 0 and 1."""
return (parameters - self.__scale_arg1) / self.__scale_arg2 + 0.5
def _ensure_constraint(self, trial):
"""Make sure the parameters lie between the limits."""
mask = np.where((trial > 1) | (trial < 0))
trial[mask] = self.random_number_generator.rand(mask[0].size)
def _mutate(self, candidate):
"""Create a trial vector based on a mutation strategy."""
trial = np.copy(self.population[candidate])
rng = self.random_number_generator
fill_point = rng.randint(0, self.parameter_count)
if self.strategy in ['currenttobest1exp', 'currenttobest1bin']:
bprime = self.mutation_func(candidate,
self._select_samples(candidate, 5))
else:
bprime = self.mutation_func(self._select_samples(candidate, 5))
if self.strategy in self._binomial:
crossovers = rng.rand(self.parameter_count)
crossovers = crossovers < self.cross_over_probability
# the last one is always from the bprime vector for binomial
# If you fill in modulo with a loop you have to set the last one to
# true. If you don't use a loop then you can have any random entry
# be True.
crossovers[fill_point] = True
trial = np.where(crossovers, bprime, trial)
return trial
elif self.strategy in self._exponential:
i = 0
while (i < self.parameter_count
and rng.rand() < self.cross_over_probability):
trial[fill_point] = bprime[fill_point]
fill_point = (fill_point + 1) % self.parameter_count
i += 1
return trial
def _best1(self, samples):
"""best1bin, best1exp"""
r0, r1 = samples[:2]
return (self.population[0] + self.scale *
(self.population[r0] - self.population[r1]))
def _rand1(self, samples):
"""rand1bin, rand1exp"""
r0, r1, r2 = samples[:3]
return (self.population[r0] + self.scale *
(self.population[r1] - self.population[r2]))
def _randtobest1(self, samples):
"""randtobest1bin, randtobest1exp"""
r0, r1, r2 = samples[:3]
bprime = np.copy(self.population[r0])
bprime += self.scale * (self.population[0] - bprime)
bprime += self.scale * (self.population[r1] - self.population[r2])
return bprime
def _currenttobest1(self, candidate, samples):
"""currenttobest1bin, currenttobest1exp"""
r0, r1 = samples[:2]
bprime = (self.population[candidate] + self.scale *
(self.population[0] - self.population[candidate] +
self.population[r0] - self.population[r1]))
return bprime
def _best2(self, samples):
"""best2bin, best2exp"""
r0, r1, r2, r3 = samples[:4]
bprime = (self.population[0] + self.scale *
(self.population[r0] + self.population[r1] -
self.population[r2] - self.population[r3]))
return bprime
def _rand2(self, samples):
"""rand2bin, rand2exp"""
r0, r1, r2, r3, r4 = samples
bprime = (self.population[r0] + self.scale *
(self.population[r1] + self.population[r2] -
self.population[r3] - self.population[r4]))
return bprime
def _select_samples(self, candidate, number_samples):
"""
obtain random integers from range(self.num_population_members),
without replacement. You can't have the original candidate either.
"""
idxs = list(range(self.num_population_members))
idxs.remove(candidate)
self.random_number_generator.shuffle(idxs)
idxs = idxs[:number_samples]
return idxs
