mirror of
https://github.com/vale981/ray
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108 lines
3.8 KiB
Python
108 lines
3.8 KiB
Python
"""This file is used for specifying various schedules that evolve over
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time throughout the execution of the algorithm, such as:
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- learning rate for the optimizer
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- exploration epsilon for the epsilon greedy exploration strategy
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- beta parameter for beta parameter in prioritized replay
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Each schedule has a function `value(t)` which returns the current value
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of the parameter given the timestep t of the optimization procedure.
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"""
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from __future__ import absolute_import
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from __future__ import division
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from __future__ import print_function
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class Schedule(object):
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def value(self, t):
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"""Value of the schedule at time t"""
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raise NotImplementedError()
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class ConstantSchedule(object):
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def __init__(self, value):
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"""Value remains constant over time.
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Parameters
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----------
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value: float
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Constant value of the schedule
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"""
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self._v = value
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def value(self, t):
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"""See Schedule.value"""
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return self._v
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def linear_interpolation(l, r, alpha):
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return l + alpha * (r - l)
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class PiecewiseSchedule(object):
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def __init__(self,
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endpoints,
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interpolation=linear_interpolation,
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outside_value=None):
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"""Piecewise schedule.
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endpoints: [(int, int)]
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list of pairs `(time, value)` meanining that schedule should output
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`value` when `t==time`. All the values for time must be sorted in
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an increasing order. When t is between two times, e.g.
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`(time_a, value_a)`
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and `(time_b, value_b)`, such that `time_a <= t < time_b` then value
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outputs `interpolation(value_a, value_b, alpha)` where alpha is a
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fraction of time passed between `time_a` and `time_b` for time `t`.
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interpolation: lambda float, float, float: float
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a function that takes value to the left and to the right of t
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according to the `endpoints`. Alpha is the fraction of distance from
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left endpoint to right endpoint that t has covered. See
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linear_interpolation for example.
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outside_value: float
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if the value is requested outside of all the intervals sepecified in
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`endpoints` this value is returned. If None then AssertionError is
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raised when outside value is requested.
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"""
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idxes = [e[0] for e in endpoints]
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assert idxes == sorted(idxes)
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self._interpolation = interpolation
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self._outside_value = outside_value
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self._endpoints = endpoints
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def value(self, t):
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"""See Schedule.value"""
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for (l_t, l), (r_t, r) in zip(self._endpoints[:-1],
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self._endpoints[1:]):
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if l_t <= t and t < r_t:
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alpha = float(t - l_t) / (r_t - l_t)
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return self._interpolation(l, r, alpha)
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# t does not belong to any of the pieces, so doom.
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assert self._outside_value is not None
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return self._outside_value
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class LinearSchedule(object):
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def __init__(self, schedule_timesteps, final_p, initial_p=1.0):
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"""Linear interpolation between initial_p and final_p over
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schedule_timesteps. After this many timesteps pass final_p is
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returned.
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Parameters
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----------
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schedule_timesteps: int
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Number of timesteps for which to linearly anneal initial_p
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to final_p
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initial_p: float
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initial output value
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final_p: float
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final output value
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"""
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self.schedule_timesteps = schedule_timesteps
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self.final_p = final_p
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self.initial_p = initial_p
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def value(self, t):
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"""See Schedule.value"""
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fraction = min(float(t) / max(1, self.schedule_timesteps), 1.0)
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return self.initial_p + fraction * (self.final_p - self.initial_p)
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