Cell Attributes
---------------

Each cell in a population has several **attributes** that
characterise its anatomical and physiological properties.  These are:


* **ori** - orientation, 0..180.0

* **dir** - direction, 0..360.0 (this is stored as 'ori', but can be
           referred to as 'dir' when the relevant values go from
           0..360)

* **ori_cv** - circular variance of orientation 0..1

* **phase** - phase of spatial RF, 0..360.0

* **ocdom** - ocular dominance, -1.0 (left) to 1.0 (right)

* **rfx, rfy** - position of center of RF on LGN/stimulus grid (xn by yn)

* **cx, cy** - cortical location in microns


Some attributes can be rederived after an input is connected to a cell
using the following commands in the body of an <input> object:


* **attr_ori_derive_from_pop [pop_name]** - to compute the orifrom the
  ori values of all synaptic inputs from the named population,
  weighted by the synaptic weights.

* **attr_dir_derive_from_pop [pop_name]** - to compute the ori as a
  direction value (0..360) from the ori values and synaptic
  interactions (e.g. as DS02 with negative phase shift will add 180 to
  the input ori values).