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#genetic algorithm scaling routines
#based on galib.
from numpy import clip, inf
from ga_util import GAError, my_mean, my_std
# if a score is less the 2 standard deviations below, the average, its score
# is arbitrarily set to zero
class sigma_truncation_scaling(object):
def __init__(self, scaling = 2):
self.scaling = scaling
def scale(self, pop):
sc = pop.scores()
avg = my_mean(sc)
if len(sc) > 1:
dev = my_std(sc)
else:
dev = 0
f = clip(sc - avg + self.scaling * dev, 0, inf)
for i in range(len(pop)):
pop[i].fitness(f[i])
return pop
class no_scaling(object):
def scale(self,pop):
for ind in pop:
ind.fitness(ind.score())
return pop
class linear_scaling(object):
def __init__(self,mult = 1.2):
self.mult = mult
def scale(self,pop):
sc = pop.scores()
pmin = min(sc)
if pmin < 0:
raise GAError('linear scaling does not work with objective scores < 0')
pmax = max(sc)
pavg = my_mean(sc)
if pavg == pmax:
a = 1.
b = 0.
elif pmin > (self.mult * pavg - pmax)/(self.mult - 1.):
delta = pmax - pavg
a = (self.mult - 1.) * pavg / delta
b = pavg * (pmax - self.mult * pavg) / delta
else:
delta = pavg - pmin
a = pavg / delta
b = -pmin * pavg / delta
f = clip(sc * a + b, 0, inf)
for i in range(len(pop)):
pop[i].fitness(f[i])
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