**Name:**

topology::Displacement - compute displacement vector

**Synopsis:**

from_gid to_gid Displacement -> [double vector]

from_pos to_gid Displacement -> [double vector]

**Description:**

This function returns a vector connecting the position of the "from_gid"

node or the explicitly given "from_pos" position and the position of the

"to_gid" node. Nodes must be parts of topology layers.

The "from" position is projected into the layer of the "to_gid" node. If

this layer has periodic boundary conditions (EdgeWrap is true), then the

shortest displacement vector is returned, taking into account the

periodicity. Fixed grid layers are in this case extended so that the

nodes at the edges of the layer have a distance of one grid unit when

wrapped.

Example:

topology using

<< /rows 5

/columns 4

/elements /iaf_psc_alpha

>> CreateLayer ;

4 5 Displacement

[0.2 0.3] 5 Displacement

**Parameters:**

from_gid - int, gid of node in a topology layer

from_pos - double vector, position in layer

to_gid - int, gid of node in a topology layer

Returns:

[double vector] - vector pointing from position "from" to position "to"

**Author:**

HÃ¥kon Enger, Hans E Plesser, Kittel Austvoll

See also: Distance, GetPosition

**Source:**

/home/graber/work-nest/nest-git/nest-simulator/topology/topologymodule.cpp