# Distance functions¶

Distance functions which measure closeness of observed and sampled data. For custom distance functions, either pass a plain function to ABCSMC or subclass the DistanceFunction class if finer grained configuration is required.

class pyabc.distance_functions.AcceptAllDistance

Just a mock distance function which always returns -1. So any sample should be accepted for any sane epsilon object.

Can be used for testing.

__call__(x, y)
Parameters: x (dictionary) – sample point y (dictionary) – measured point
class pyabc.distance_functions.DistanceFunction

Bases: abc.ABC

Abstract case class for distance functions.

Any other distance function should inherit from this class.

__call__(x: dict, x_0: dict) → float

Abstract method. This method has to be overwritten by all concrete implementations.

Evaluate the distance of the tentatively samples particle to the measured data.

Parameters: x (dict) – Summary statistics of the tentatively sampled parameter. x_0 (dict) – Summary statistics of the measured data. distance – Attributes distance of the tentatively sampled particle from the measured data. float
get_config() → dict

Return configuration of the distance function.

Returns: config – Dictionary describing the distance function. dict
initialize(sample_from_prior: List[dict])

This method is called by the ABCSMC framework before the first usage of the distance function and can be used to calibrate it to the statistics of the samples.

The default implementation is to do nothing.

Parameters: sample_from_prior (List[dict]) – List of dictionaries containng the summary statistics.
to_json() → str

Return JSON encoded configuration of the distance function.

Returns: json_str – JSON encoded string describing the distance function. The default implementation is to try to convert the dictionary returned my get_config. str
class pyabc.distance_functions.DistanceFunctionWithMeasureList(measures_to_use='all')

Base class for distance functions with measure list. This class is not functional on its own.

Parameters: measures_to_use (Union[str, List[str]]) – If set to “all”, all measures are used. This is the default If a list is provided, the measures in the list are used. measures refers to the summary statistics.
get_config()

Return configuration of the distance function.

Returns: config – Dictionary describing the distance function. dict
initialize(sample_from_prior)

This method is called by the ABCSMC framework before the first usage of the distance function and can be used to calibrate it to the statistics of the samples.

The default implementation is to do nothing.

Parameters: sample_from_prior (List[dict]) – List of dictionaries containng the summary statistics.
measures_to_use = None

The measures (summary statistics) to use for distance calculation.

class pyabc.distance_functions.IdentityFakeDistance

A fake distance function, which just passes the summary statistics on. This class assumes, that the model already returns the distance. This can be useful in cases where simulating can be stopped early when during the simulation some condition is reached which makes it impossible to accept the particle.

__call__(x, y)

Abstract method. This method has to be overwritten by all concrete implementations.

Evaluate the distance of the tentatively samples particle to the measured data.

Parameters: x (dict) – Summary statistics of the tentatively sampled parameter. x_0 (dict) – Summary statistics of the measured data. distance – Attributes distance of the tentatively sampled particle from the measured data. float
class pyabc.distance_functions.MinMaxDistanceFunction(measures_to_use='all')

Calculate upper and lower margins as max and min of the parameters. This works surprisingly well for normalization in simple cases

static lower()

Calculate the lower margin form a list of parameter values.

Parameters: parameter_list (List[float]) – List of values of a parameter. lower_margin – The lower margin of the range calculated from these parameters float
static upper()

Calculate the upper margin form a list of parameter values.

Parameters: parameter_list (List[float]) – List of values of a parameter. upper_margin – The upper margin of the range calculated from these parameters float
class pyabc.distance_functions.NoDistance

Implements a kind of null object as distance function.

__call__(x: dict, x_0: dict) → float

Abstract method. This method has to be overwritten by all concrete implementations.

Evaluate the distance of the tentatively samples particle to the measured data.

Parameters: x (dict) – Summary statistics of the tentatively sampled parameter. x_0 (dict) – Summary statistics of the measured data. distance – Attributes distance of the tentatively sampled particle from the measured data. float
class pyabc.distance_functions.PCADistanceFunction(measures_to_use='all')

Calculate distance in whitened coordinates.

A whitening transformation $$X$$ is calculated from an initial sample. The distance is measured as euclidean distance in the transformed space. I.e

$d(x,y) = \| Wx - Wy \|$
__call__(x, y)

Abstract method. This method has to be overwritten by all concrete implementations.

Evaluate the distance of the tentatively samples particle to the measured data.

Parameters: x (dict) – Summary statistics of the tentatively sampled parameter. x_0 (dict) – Summary statistics of the measured data. distance – Attributes distance of the tentatively sampled particle from the measured data. float
initialize(sample_from_prior)

This method is called by the ABCSMC framework before the first usage of the distance function and can be used to calibrate it to the statistics of the samples.

The default implementation is to do nothing.

Parameters: sample_from_prior (List[dict]) – List of dictionaries containng the summary statistics.
class pyabc.distance_functions.PercentileDistanceFunction(measures_to_use='all')

Calculate normalization 20% and 80% from percentiles as lower and upper margins

PERCENTILE = 20

The percentiles

get_config()

Return configuration of the distance function.

Returns: config – Dictionary describing the distance function. dict
static lower()

Calculate the lower margin form a list of parameter values.

Parameters: parameter_list (List[float]) – List of values of a parameter. lower_margin – The lower margin of the range calculated from these parameters float
static upper()

Calculate the upper margin form a list of parameter values.

Parameters: parameter_list (List[float]) – List of values of a parameter. upper_margin – The upper margin of the range calculated from these parameters float
class pyabc.distance_functions.RangeEstimatorDistanceFunction(measures_to_use='all')

Abstract base class for distance functions which estimate is based on a range.

It defines the two template methods lower and upper.

Hence

$d(x, y) = \sum_{i \in \text{measures}} \left | \frac{x_i - y_i}{u_i - l_i} \right |$

where $$l_i$$ and $$u_i$$ are the lower and upper margin for measure $$i$$.

__call__(x, y)

Abstract method. This method has to be overwritten by all concrete implementations.

Evaluate the distance of the tentatively samples particle to the measured data.

Parameters: x (dict) – Summary statistics of the tentatively sampled parameter. x_0 (dict) – Summary statistics of the measured data. distance – Attributes distance of the tentatively sampled particle from the measured data. float
get_config()

Return configuration of the distance function.

Returns: config – Dictionary describing the distance function. dict
initialize(sample_from_prior)

This method is called by the ABCSMC framework before the first usage of the distance function and can be used to calibrate it to the statistics of the samples.

The default implementation is to do nothing.

Parameters: sample_from_prior (List[dict]) – List of dictionaries containng the summary statistics.
static lower()

Calculate the lower margin form a list of parameter values.

Parameters: parameter_list (List[float]) – List of values of a parameter. lower_margin – The lower margin of the range calculated from these parameters float
static upper()

Calculate the upper margin form a list of parameter values.

Parameters: parameter_list (List[float]) – List of values of a parameter. upper_margin – The upper margin of the range calculated from these parameters float
class pyabc.distance_functions.SimpleFunctionDistance(function)

This is a wrapper around a simple function which calculates the distance. If a function is passed to the ABCSMC class, then it is converted to an instance of the SimpleFunctionDistance class.

__call__(x, y)

Abstract method. This method has to be overwritten by all concrete implementations.

Evaluate the distance of the tentatively samples particle to the measured data.

Parameters: x (dict) – Summary statistics of the tentatively sampled parameter. x_0 (dict) – Summary statistics of the measured data. distance – Attributes distance of the tentatively sampled particle from the measured data. float
get_config()

Return configuration of the distance function.

Returns: config – Dictionary describing the distance function. dict
class pyabc.distance_functions.ZScoreDistanceFunction(measures_to_use='all')

Calculate distance as sum of ZScore over the selected measures. The measured Data is the reference for the ZScore.

Hence

$d(x, y) = \sum_{i \in \text{measures}} \left| \frac{x_i-y_i}{y_i} \right|$
__call__(x, y)

Abstract method. This method has to be overwritten by all concrete implementations.

Evaluate the distance of the tentatively samples particle to the measured data.

Parameters: x (dict) – Summary statistics of the tentatively sampled parameter. x_0 (dict) – Summary statistics of the measured data. distance – Attributes distance of the tentatively sampled particle from the measured data. float
pyabc.distance_functions.to_distance(maybe_distance_function)
Parameters: maybe_distance_function (either a callable, which takes two arguments or) – DistanceFunction instance (a) –