# Source code for stonesoup.measures.state

import copy
from abc import abstractmethod
from functools import lru_cache

import numpy as np
from scipy.spatial import distance

from .base import BaseMeasure
from ..base import Property
from ..types.state import State, ParticleState, GaussianState

[docs]
class Measure(BaseMeasure):
"""Measure base type

A measure provides a means to assess the separation between two
:class:~.State objects state1 and state2.
"""
mapping: np.ndarray = Property(
default=None,
doc="Mapping array which specifies which elements within the"
" state vectors are to be assessed as part of the measure"
)
mapping2: np.ndarray = Property(
default=None,
doc="A second mapping for when the states being compared exist "
"in different parameter spaces. Defaults to the same as the"
" first mapping"
)

[docs]
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if self.mapping2 is not None and self.mapping is None:
raise ValueError("Cannot set mapping2 if mapping is None. "
"If this is really what you meant to do, then"
" set mapping to include all dimensions.")
if self.mapping2 is None and self.mapping is not None:
self.mapping2 = self.mapping

[docs]
@abstractmethod
def __call__(self, state1, state2):
r"""
Compute the distance between a pair of :class:~.State objects

Parameters
----------
state1 : :class:~.State
state2 : :class:~.State

Returns
-------
float
distance measure between a pair of input :class:~.State objects

"""
return NotImplementedError

[docs]
class Euclidean(Measure):
r"""Euclidean distance measure

This measure returns the Euclidean distance between a pair of
:class:~.State objects.

The Euclidean distance between a pair of state vectors :math:u and
:math:v is defined as:

.. math::
\sqrt{\sum_{i=1}^{N}{(u_i - v_i)^2}}

"""

[docs]
def __call__(self, state1, state2):
r"""Calculate the Euclidean distance between a pair of state vectors

Parameters
----------
state1 : :class:~.State
state2 : :class:~.State

Returns
-------
float
Euclidean distance between two input :class:~.State

"""
# Calculate Euclidean distance between two state
state_vector1 = getattr(state1, 'mean', state1.state_vector)
state_vector2 = getattr(state2, 'mean', state2.state_vector)

if self.mapping is not None:
return distance.euclidean(state_vector1[self.mapping, 0],
state_vector2[self.mapping2, 0])
else:
return distance.euclidean(state_vector1[:, 0], state_vector2[:, 0])

[docs]
class EuclideanWeighted(Measure):
r"""Weighted Euclidean distance measure

This measure returns the Euclidean distance between a pair of
:class:~.State objects, taking into account a specified weighting.

The Weighted Euclidean distance between a pair of state vectors :math:u
and :math:v with weighting :math:w is defined as:

.. math::
\sqrt{\sum_{i=1}^{N}{w_i|(u_i - v_i)^2}}

Note
----
The EuclideanWeighted object has a property called weighting, which
allows the method to be called on different pairs of states.
If different weightings need to be used then multiple
:class:Measure objects must be created with the specific weighting

"""
weighting: np.ndarray = Property(doc="Weighting vector for the Euclidean calculation")

[docs]
def __call__(self, state1, state2):
r"""Calculate the weighted Euclidean distance between a pair of state
objects

Parameters
----------
state1 : :class:~.State
state2 : :class:~.State

Returns
-------
dist : float
Weighted euclidean distance between two input
:class:~.State objects

"""
state_vector1 = getattr(state1, 'mean', state1.state_vector)
state_vector2 = getattr(state2, 'mean', state2.state_vector)

if self.mapping is not None:
return distance.euclidean(state_vector1[self.mapping, 0],
state_vector2[self.mapping2, 0],
self.weighting)
else:
return distance.euclidean(state_vector1[:, 0],
state_vector2[:, 0],
self.weighting)

[docs]
class SquaredMahalanobis(Measure):
r"""Squared Mahalanobis distance measure

This measure returns the Squared Mahalanobis distance between a pair of
:class:~.State objects taking into account the distribution (i.e.
the :class:~.CovarianceMatrix) of the first :class:.State object

The Squared Mahalanobis distance between a distribution with mean :math:\mu
and Covariance matrix :math:\Sigma and a point :math:x is defined as:

.. math::
( {\mu - x})  \Sigma^{-1}  ({\mu - x}^T )

"""
state_covar_inv_cache_size: int = Property(
default=128,
doc="Number of covariance matrix inversions to cache. Setting to 0 will disable the "
"cache, whilst setting to None will not limit the size of the cache. Default is "
"128.")

[docs]
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if self.state_covar_inv_cache_size is None or self.state_covar_inv_cache_size > 0:
self._inv_cov = lru_cache(maxsize=self.state_covar_inv_cache_size)(self._inv_cov)

[docs]
def __getstate__(self):
result = copy.copy(self.__dict__)
result["_inv_cov"] = None
return result

def __setstate__(self, state):
self.__dict__ = state
if self.state_covar_inv_cache_size is None or self.state_covar_inv_cache_size > 0:
self._inv_cov = lru_cache(maxsize=self.state_covar_inv_cache_size)(type(self)._inv_cov)
else:
self._inv_cov = type(self)._inv_cov

[docs]
def __call__(self, state1, state2):
r"""Calculate the Squared Mahalanobis distance between a pair of state objects

Parameters
----------
state1 : :class:~.State
state2 : :class:~.State

Returns
-------
float
Squared Mahalanobis distance between a pair of input :class:~.State
objects

"""
state_vector1 = getattr(state1, 'mean', state1.state_vector)
state_vector2 = getattr(state2, 'mean', state2.state_vector)

if self.mapping is not None:
u = state_vector1[self.mapping, 0]
v = state_vector2[self.mapping2, 0]
# extract the mapped covariance data
vi = self._inv_cov(state1, tuple(self.mapping))
else:
u = state_vector1[:, 0]
v = state_vector2[:, 0]
vi = self._inv_cov(state1)

delta = u - v

return np.dot(np.dot(delta, vi), delta)

@staticmethod
def _inv_cov(state, mapping=None):
if mapping:
rows = np.array(mapping, dtype=np.intp)
columns = np.array(mapping, dtype=np.intp)
covar = state.covar[rows[:, np.newaxis], columns]
else:
covar = state.covar

return np.linalg.inv(covar)

[docs]
class Mahalanobis(SquaredMahalanobis):
r"""Mahalanobis distance measure

This measure returns the Mahalanobis distance between a pair of
:class:~.State objects taking into account the distribution (i.e.
the :class:~.CovarianceMatrix) of the first :class:.State object

The Mahalanobis distance between a distribution with mean :math:\mu and
Covariance matrix :math:\Sigma and a point :math:x is defined as:

.. math::
\sqrt{( {\mu - x})  \Sigma^{-1}  ({\mu - x}^T )}

"""

[docs]
def __call__(self, state1, state2):
r"""Calculate the Mahalanobis distance between a pair of state objects

Parameters
----------
state1 : :class:~.State
state2 : :class:~.State

Returns
-------
float
Mahalanobis distance between a pair of input :class:~.State
objects

"""
return np.sqrt(super().__call__(state1, state2))

[docs]
class SquaredGaussianHellinger(Measure):
r"""Squared Gaussian Hellinger distance measure

This measure returns the Squared Hellinger distance between a pair of
:class:~.GaussianState multivariate objects.

The Squared Hellinger distance between two multivariate normal
distributions :math:P \sim N(\mu_1,\Sigma_1) and
:math:Q \sim N(\mu_2,\Sigma_2) is defined as:

.. math::
H^{2}(P, Q) &= 1 - {\frac{\det(\Sigma_1)^{\frac{1}{4}}\det(\Sigma_2)^{\frac{1}{4}}}
{\det\left(\frac{\Sigma_1+\Sigma_2}{2}\right)^{\frac{1}{2}}}}
\exp\left(-\frac{1}{8}(\mu_1-\mu_2)^T
\left(\frac{\Sigma_1+\Sigma_2}{2}\right)^{-1}(\mu_1-\mu_2)\right)\\
&\equiv  1 - \sqrt{\frac{\det(\Sigma_1)^{\frac{1}{2}}\det(\Sigma_2)^{\frac{1}{2}}}
{\det\left(\frac{\Sigma_1+\Sigma_2}{2}\right)}}
\exp\left(-\frac{1}{8}(\mu_1-\mu_2)^T
\left(\frac{\Sigma_1+\Sigma_2}{2}\right)^{-1}(\mu_1-\mu_2)\right)

Note
----
This distance is bounded between 0 and 1
"""

[docs]
def __call__(self, state1, state2):
r""" Calculate the Squared Hellinger distance multivariate normal
distributions

Parameters
----------
state1 : :class:~.GaussianState
state2 : :class:~.GaussianState

Returns
-------
float
Squared Hellinger distance between two input
:class:~.GaussianState

"""
if hasattr(state1, 'mean'):
state_vector1 = state1.mean
else:
state_vector1 = state1.state_vector

if hasattr(state2, 'mean'):
state_vector2 = state2.mean
else:
state_vector2 = state2.state_vector

if self.mapping is not None:
mu1 = state_vector1[self.mapping, :]
mu2 = state_vector2[self.mapping2, :]

# extract the mapped covariance data
rows = np.array(self.mapping, dtype=np.intp)
columns = np.array(self.mapping, dtype=np.intp)
sigma1 = state1.covar[rows[:, np.newaxis], columns]
sigma2 = state2.covar[rows[:, np.newaxis], columns]
else:
mu1 = state_vector1
mu2 = state_vector2
sigma1 = state1.covar
sigma2 = state2.covar

sigma1_plus_sigma2 = sigma1 + sigma2
mu1_minus_mu2 = mu1 - mu2
E = mu1_minus_mu2.T @ np.linalg.inv(sigma1_plus_sigma2/2) @ mu1_minus_mu2
epsilon = -0.125*E
numerator = np.sqrt(np.linalg.det(sigma1 @ sigma2))
denominator = np.linalg.det(sigma1_plus_sigma2/2)
squared_hellinger = 1 - np.sqrt(numerator/denominator)*np.exp(epsilon)
squared_hellinger = squared_hellinger.item()

if -1e-10 < squared_hellinger < 0.0:
squared_hellinger = 0.0
elif squared_hellinger < 0.0:  # pragma: no cover
raise ValueError("Measure shouldn't be less than 0")  # this should be impossible

return squared_hellinger

[docs]
class GaussianHellinger(SquaredGaussianHellinger):
r"""Gaussian Hellinger distance measure

This measure returns the Hellinger distance between a pair of
:class:~.GaussianState multivariate objects.

The Hellinger distance between two multivariate normal distributions
:math:P \sim N(\mu_1,\Sigma_1) and :math:Q \sim N(\mu_2,\Sigma_2)
is defined as:

.. math::
H(P,Q) = \sqrt{1 - {\frac{\det(\Sigma_1)^{\frac{1}{4}}\det(\Sigma_2)^{\frac{1}{4}}}
{\det\left(\frac{\Sigma_1+\Sigma_2}{2}\right)^{\frac{1}{2}}}}
\exp\left(-\frac{1}{8}(\mu_1-\mu_2)^T
\left(\frac{\Sigma_1+\Sigma_2}{2}\right)^{-1}(\mu_1-\mu_2)\right)}

Note
----
This distance is bounded between 0 and 1
"""

[docs]
def __call__(self, state1, state2):
r""" Calculate the Hellinger distance between 2 state elements

Parameters
----------
state1 : :class:~.GaussianState
state2 : :class:~.GaussianState

Returns
-------
float
Hellinger distance between two input :class:~.GaussianState

"""
return np.sqrt(super().__call__(state1, state2))

[docs]
class ObservationAccuracy(Measure):
r"""Accuracy measure

This measure evaluates the accuracy of a categorical distribution with respect to another."""

[docs]
def __call__(self, state1, state2):

if isinstance(state1, State):
s1 = state1.state_vector
else:
s1 = state1

if isinstance(state2, State):
s2 = state2.state_vector
else:
s2 = state2

mins = [min(s1, s2) for s1, s2 in zip(s1, s2)]
maxs = [max(s1, s2) for s1, s2 in zip(s1, s2)]
return np.sum(mins)/np.sum(maxs)

[docs]
class KLDivergence(Measure):
r"""Kullback-Leibler divergence between two distributions

Kullback-Leibler divergence, also referred to as relative entropy, is a
statistical distance. It describes how a probability distribution is
different from another. The expression for Kullback-Leibler divergence
is given by [1]_

.. math::
D_{KL}(P\Vert Q) = \sum_x P(x)\log \frac{P(x)}{Q(x)},

where :math:P(x) is the first distribution, or state1 and :math:Q(x)
is the second distribution or, state2. It is worth noting that Kullback-Leibler
divergence is not symmetric under interchange of :math:P(x) and :math:Q(x). The
implementation here uses natural log meaning the returned divergence has units in nats.
This implementation assumes a discrete probability space and currently only accepts
:class:~.ParticleState.

References
----------
.. [1] MacKay, David J. C. 2003. Information Theory, Inference and Learning
Algorithms, 1st Ed. Cambridge University Press, """

[docs]
def __call__(self, state1, state2):
r"""
Computes the Kullback–Leibler divergence from state1 to state2

Parameters
----------
state1 : :class:~.ParticleState
state2 : :class:~.ParticleState

Returns
-------
float
Kullback–Leibler divergence from state1 to state2

"""
if isinstance(state1, ParticleState) and isinstance(state2, ParticleState):
if len(state1.particles) == len(state2.particles):

log_term = np.zeros(state1.log_weight.shape)

invalid_indx = (np.isinf(state1.log_weight) | np.isnan(state1.log_weight)
| np.isinf(state2.log_weight) | np.isnan(state2.log_weight))

# Do not consider NANs and inf in the subtraction
log_term[~invalid_indx] = state1.log_weight[~invalid_indx] \
- state2.log_weight[~invalid_indx]

kld = np.sum(np.exp(state1.log_weight)*log_term)
else:
raise ValueError(f'The input sizes are not compatible '
f'({len(state1.particles)} != {len(state2.particles)})')

elif isinstance(state1, GaussianState) and isinstance(state2, GaussianState):

state1 = copy.copy(state1)
state2 = copy.copy(state2)

if self.mapping is not None:
state1.state_vector = state1.state_vector[self.mapping, :]
state2.state_vector = state2.state_vector[self.mapping2, :]

rows = np.array(self.mapping, dtype=np.intp)
columns = np.array(self.mapping, dtype=np.intp)
state1.covar = state1.covar[rows[:, np.newaxis], columns]

rows2 = np.array(self.mapping2, dtype=np.intp)
columns2 = np.array(self.mapping2, dtype=np.intp)
state2.covar = state2.covar[rows2[:, np.newaxis], columns2]

if state1.ndim == state2.ndim:

log_term = np.log(np.linalg.det(state2.covar) / np.linalg.det(state1.covar))

n_dims = state1.ndim

inv_state2_covar = np.linalg.inv(state2.covar)
trace_term = np.trace(inv_state2_covar@state1.covar)

delta = state2.state_vector - state1.state_vector
mahalanobis_term = delta.T @ inv_state2_covar @ delta

kld = float(0.5*(log_term - n_dims + trace_term + mahalanobis_term))

else:
raise ValueError(f'The state dimensions are not compatible '
f'({state1.ndim} != {state2.ndim}')

else:
raise NotImplementedError('This measure is currently only compatible with '
'ParticleState or GaussianState types')

return kld