:orphan:

mu
**

Specifies the genetic predisposition for responding with certain behaviors to certain stimulus elements.
The parameter ``mu`` works in conjunction with :doc:`beta` to determine the weights for behaviors 
in :ref:`the decision function<the-decision-function>`.

The parameter ``mu`` can be set to certain values for certain particular element-behavior pairs.
It can also be specified as a single value, in which case the same predisposition is used for all
element-behavior pairs. Wildcards (*) may be used to set several values at once.

Syntax
------

::

  mu = e1->b1: v1, e1->b2: v2, ..., en->bn: vn, default: d
  mu = v1
  mu = *->*:v1  # Same as above
  mu = e1->*:v1
  mu = *->b1:v1  

where ``v1,v2,...,vn`` and ``d`` are :ref:`scalar expressions<scalar-expressions>`.

Description
-----------

``mu = e1->b1: v1, e1->b2: v2, ..., en->bn: vn, default: d`` sets the genetic predisposition value for

- e1->b1 to v1,
- e1->b2 to v2, ...,
- en->bn to v2,

and the value for all other element-behavior pairs to d.

- The specification is independent of the list order:

  ``mu = e1->b1:v1, e1->b2:v2, default:d``

  is the same as

  ``mu = e1->b2:v2, default:d, e1->b1:v1``.

- ``default`` need not be specified if all possible combinations ``element->behavior`` are present in the list. For example,

  ::

    stimulus_elements = e1, e2
    behaviors = b1, b2
    mu = e1->b1:v11, e1->b2:v12, e2->b1:v21, e2->b2:v22

----

``mu = v1`` sets the genetic predisposition value for all element-behavior pairs to v1.

- ``mu = v1`` is the same as ``mu = default: v1``.

Dependencies
------------

- The properties ``stimulus_elements`` and  ``behaviors`` must be specified before ``mu``.
- Each stimulus element used in the specification of ``mu`` must be present in the parameter ``stimulus_elements``.
- Each behavior used in the specification of ``mu`` must be present in the parameter ``behaviors``.

Examples
--------

::

  @variables x = 1
  mu = element1->behavior1: x, element1->behavior2: x+1, default:x+2

sets the genetic predisposition value for element1->behavior1 to 1 and for element1->behavior1 to 2, and
for the remaining possible element-behavior pairs to 3.

::

  mu = element1->behavior1: 0.5, default:0

sets the genetic prediposition value for element1->behavior1 to 0.5, and for the remaining possible element-behavior pairs to 3.

::

  mu = 0.1

sets the genetic predisposition value for all  element-behavior pairs to 0.1.
