Parameter

class astropy.modeling.Parameter(name=u'', description=u'', default=None, getter=None, setter=None, fixed=False, tied=False, min=None, max=None, bounds=None, model=None)

Bases: object

Wraps individual parameters.

This class represents a model’s parameter (in a somewhat broad sense). It acts as both a descriptor that can be assigned to a class attribute to describe the parameters accepted by an individual model (this is called an “unbound parameter”), or it can act as a proxy for the parameter values on an individual model instance (called a “bound parameter”).

Parameter instances never store the actual value of the parameter directly. Rather, each instance of a model stores its own parameters as either hidden attributes or (in the case of FittableModel) in an array. A bound Parameter simply wraps the value in a Parameter proxy which provides some additional information about the parameter such as its constraints.

Unbound Parameters are not associated with any specific model instance, and are merely used by model classes to determine the names of their parameters and other information about each parameter such as their default values and default constraints.

Parameters:

name : str

parameter name

description : str

parameter description

default : float or array

default value to use for this parameter

getter : callable

a function that wraps the raw (internal) value of the parameter when returning the value through the parameter proxy (eg. a parameter may be stored internally as radians but returned to the user as degrees)

setter : callable

a function that wraps any values assigned to this parameter; should be the inverse of getter

fixed : bool

if True the parameter is not varied during fitting

tied : callable or False

if callable is supplied it provides a way to link the value of this parameter to another parameter (or some other arbitrary function)

min : float

the lower bound of a parameter

max : float

the upper bound of a parameter

bounds : tuple

specify min and max as a single tuple–bounds may not be specified simultaneously with min or max

model : object

an instance of a Model class; this should only be used internally for creating bound Parameters

Attributes Summary

bounds	The minimum and maximum values of a parameter as a tuple
constraints	Types of constraints a parameter can have.
default	Parameter default value
fixed	Boolean indicating if the parameter is kept fixed during fitting.
max	A value used as an upper bound when fitting a parameter
min	A value used as a lower bound when fitting a parameter
name	Parameter name
shape	The shape of this parameter’s value array.
size	The size of this parameter’s value array.
tied	Indicates that this parameter is linked to another one.
value	The unadorned value proxied by this parameter

Methods Summary

copy([name, description, default, getter, ...])

Make a copy of this Parameter, overriding any of its core attributes in the process (or an exact copy).

Attributes Documentation

bounds

The minimum and maximum values of a parameter as a tuple

constraints = (u'fixed', u'tied', u'bounds')

Types of constraints a parameter can have. Excludes ‘min’ and ‘max’ which are just aliases for the first and second elements of the ‘bounds’ constraint (which is represented as a 2-tuple).

default

Parameter default value

fixed

Boolean indicating if the parameter is kept fixed during fitting.

max

A value used as an upper bound when fitting a parameter

min

A value used as a lower bound when fitting a parameter

name

Parameter name

shape

The shape of this parameter’s value array.

size

The size of this parameter’s value array.

tied

Indicates that this parameter is linked to another one.

A callable which provides the relationship of the two parameters.

value

The unadorned value proxied by this parameter

Methods Documentation

copy(name=None, description=None, default=None, getter=None, setter=None, fixed=False, tied=False, min=None, max=None, bounds=None)

Make a copy of this Parameter, overriding any of its core attributes in the process (or an exact copy).

The arguments to this method are the same as those for the Parameter initializer. This simply returns a new Parameter instance with any or all of the attributes overridden, and so returns the equivalent of:

Parameter(self.name, self.description, ...)