# Variable class¶

(Shortest import: from brian2.core.variables import Variable)

class brian2.core.variables.Variable(name, unit, owner=None, dtype=None, scalar=False, constant=False, read_only=False, dynamic=False)[source]

Bases: object

An object providing information about model variables (including implicit variables such as t or xi). This class should never be instantiated outside of testing code, use one of its subclasses instead.

Parameters: name : ‘str’ The name of the variable. Note that this refers to the original name in the owning group. The same variable may be known under other names in other groups (e.g. the variable v of a NeuronGroup is known as v_post in a Synapse connecting to the group). unit : Unit The unit of the variable. owner : Nameable, optional The object that “owns” this variable, e.g. the NeuronGroup or Synapses object that declares the variable in its model equations. Defaults to None (the value used for Variable objects without an owner, e.g. external Constants). dtype : dtype, optional The dtype used for storing the variable. Defaults to the preference core.default_scalar.dtype. scalar : bool, optional Whether the variable is a scalar value (True) or vector-valued, e.g. defined for every neuron (False). Defaults to False. constant: bool, optional : Whether the value of this variable can change during a run. Defaults to False. read_only : bool, optional Whether this is a read-only variable, i.e. a variable that is set internally and cannot be changed by the user (this is used for example for the variable N, the number of neurons in a group). Defaults to False.

Attributes

 constant Whether the variable is constant during a run dim The dimensions of this variable. dtype The dtype used for storing the variable. dtype_str String representation of the numpy dtype dynamic Whether the variable is dynamically sized (only for non-scalars) is_boolean name The variable’s name. owner The Group to which this variable belongs. read_only Whether the variable is read-only scalar Whether the variable is a scalar unit The variable’s unit.

Methods

 get_addressable_value(name, group) Get the value (without units) of this variable in a form that can be indexed in the context of a group. get_addressable_value_with_unit(name, group) Get the value (with units) of this variable in a form that can be indexed in the context of a group. get_len() Get the length of the value associated with the variable or 0 for a scalar variable. get_value() Return the value associated with the variable (without units). get_value_with_unit() Return the value associated with the variable (with units). set_value(value) Set the value associated with the variable.

Details

constant

Whether the variable is constant during a run

dim

The dimensions of this variable.

dtype

The dtype used for storing the variable.

dtype_str

String representation of the numpy dtype

dynamic

Whether the variable is dynamically sized (only for non-scalars)

is_boolean
name

The variable’s name.

owner

The Group to which this variable belongs.

read_only

scalar

Whether the variable is a scalar

unit

The variable’s unit.

get_addressable_value(name, group)[source]

Get the value (without units) of this variable in a form that can be indexed in the context of a group. For example, if a postsynaptic variable x is accessed in a synapse S as S.x_post, the synaptic indexing scheme can be used.

Parameters: name : str The name of the variable group : Group The group providing the context for the indexing. Note that this group is not necessarily the same as Variable.owner: a variable owned by a NeuronGroup can be indexed in a different way if accessed via a Synapses object. variable : object The variable in an indexable form (without units).
get_addressable_value_with_unit(name, group)[source]

Get the value (with units) of this variable in a form that can be indexed in the context of a group. For example, if a postsynaptic variable x is accessed in a synapse S as S.x_post, the synaptic indexing scheme can be used.

Parameters: name : str The name of the variable group : Group The group providing the context for the indexing. Note that this group is not necessarily the same as Variable.owner: a variable owned by a NeuronGroup can be indexed in a different way if accessed via a Synapses object. variable : object The variable in an indexable form (with units).
get_len()[source]

Get the length of the value associated with the variable or 0 for a scalar variable.

get_value()[source]

Return the value associated with the variable (without units). This is the way variables are accessed in generated code.

get_value_with_unit()[source]

Return the value associated with the variable (with units).

set_value(value)[source]

Set the value associated with the variable.