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# Source code for catalyst.tools.meters.averagevaluemeter

"""
Average value meter
"""
import numpy as np

from . import meter

[docs]class AverageValueMeter(meter.Meter):
"""
Average value meter stores mean and standard deviation
for population of input values.
Meter updates are applied online, one value for each update.
Values are not cached, only the last added.
"""

[docs]    def __init__(self):
"""Constructor method for the AverageValueMeter class."""
super(AverageValueMeter, self).__init__()
self.n = 0
self.val = 0.0
self.mean = np.nan
self.mean_old = 0.0
self.m_s = 0.0
self.std = np.nan
self.n_samples = 0

[docs]    def add(self, value, batch_size) -> None:

Updates of mean and std are going online, with
Welford's online algorithm
<https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance>_.

Args:
value (float): value for update,
can be scalar number or PyTorch tensor

.. note::
Because of algorithm design,
you can update meter values with only one value a time.
"""
self.val = value
self.n += 1
self.n_samples += batch_size

if self.n == 1:
self.mean = 0.0 + value  # Force a copy in torch/numpy
self.std = 0.0
self.mean_old = self.mean
self.m_s = 0.0
else:
self.mean = self.mean_old + (
value - self.mean_old
) * batch_size / float(self.n_samples)
self.m_s += (
(value - self.mean_old) * (value - self.mean) * batch_size
)
self.mean_old = self.mean
self.std = np.sqrt(self.m_s / (self.n_samples - 1.0))

[docs]    def value(self):
"""Returns meter values.

Returns:
mean (float): Mean that has been updated online.
std (float): Standard deviation that has been updated online.
"""
return self.mean, self.std

[docs]    def reset(self):
"""Resets the meter to default settings."""
self.n = 0
self.val = 0.0
self.mean = np.nan
self.mean_old = 0.0
self.m_s = 0.0
self.std = np.nan
self.n_samples = 0