# -*- coding: utf-8 -*-
r""" The UCBwrong policy for bounded bandits, like UCB but with a typo on the estimator of means:
:math:`\frac{X_k(t)}{t}` is used instead of :math:`\frac{X_k(t)}{N_k(t)}`.
One paper of W.Jouini, C.Moy and J.Palicot from 2009 contained this typo, I reimplemented it just to check that:
- its performance is worse than simple UCB,
- but not that bad...
"""
from __future__ import division, print_function # Python 2 compatibility
__author__ = "Lilian Besson"
__version__ = "0.1"
from math import sqrt, log
import numpy as np
np.seterr(divide='ignore') # XXX dangerous in general, controlled here!
# WARNING: this is a HUGE hack to fix a mystery bug on importing this policy
from sys import path
from os.path import dirname
path.insert(0, '/'.join(dirname(__file__).split('/')[:-1]))
try:
from .IndexPolicy import IndexPolicy
except ImportError:
from IndexPolicy import IndexPolicy
[docs]class UCBwrong(IndexPolicy):
""" The UCBwrong policy for bounded bandits, like UCB but with a typo on the estimator of means.
One paper of W.Jouini, C.Moy and J.Palicot from 2009 contained this typo, I reimplemented it just to check that:
- its performance is worse than simple UCB
- but not that bad...
"""
[docs] def computeIndex(self, arm):
r""" Compute the current index, at time t and after :math:`N_k(t)` pulls of arm k:
.. math:: I_k(t) = \frac{X_k(t)}{t} + \sqrt{\frac{2 \log(t)}{N_k(t)}}.
"""
if self.pulls[arm] < 1:
return float('+inf')
else:
# XXX Volontary typo, wrong mean estimate
return (self.rewards[arm] / self.t) + sqrt((2 * log(self.t)) / self.pulls[arm])
[docs] def computeAllIndex(self):
""" Compute the current indexes for all arms, in a vectorized manner."""
indexes = (self.rewards / self.t) + np.sqrt((2 * np.log(self.t)) / self.pulls)
indexes[self.pulls < 1] = float('+inf')
self.index[:] = indexes