spike_generator


Name:
spike_generator - A device which generates spikes from an array with  
spike-times.
Synopsis:
spike_generator Create -> gid  

Description:
 
A spike generator can be used to generate spikes at specific times
which are given to the spike generator as an array.

Spike times are given in milliseconds, and must be sorted with the
earliest spike first. All spike times must be strictly in the future.
Trying to set a spike time in the past or at the current time step,
will cause a NEST error. Setting a spike time of 0.0 will also result
in an error.

Spike times may not coincide with a time step, i.e., are not a multiple
of the simulation resolution. Three options control how spike times that
do not coincide with a step are handled (see examples below):

Multiple occurences of the same time indicate that more than one
event is to be generated at this particular time.

Additionally, spike_weights can be set. This also is an array,
which contains one weight value per spike time. If set, the spikes
are delivered with the respective weight multiplied with the
weight of the connection. To disable this functionality, the
spike_weights array can be set to an empty array.

/precise_times default: false
If false, spike times will be rounded to simulation steps, i.e., multiples
of the resolution. The rounding is controlled by the two other flags.
If true, spike times will not be rounded but represented exactly as a
combination of step and offset. This should only be used if all neurons
receiving the spike train can handle precise timing information. In this
case, the other two options are ignored.

/allow_offgrid_times default: false
If false, spike times will be rounded to the nearest step if they are
less than tic/2 from the step, otherwise NEST reports an error.
If true, spike times are rounded to the nearest step if within tic/2
from the step, otherwise they are rounded up to the *end* of the step.

/shift_now_spikes default: false
This option is mainly for use by the PyNN-NEST interface.
If false, spike times rounded down to the current point in time will
be considered in the past and ignored.
If true, spike times that are rounded down to the current time step
are shifted one time step into the future.

Note that GetStatus will report the spike times that the spike_generator
will actually use, i.e., for grid-based simulation the spike times rounded
to the appropriate point on the time grid. This means that GetStatus may
return different /spike_times values at different resolutions.

Example:
spikegenerator << /spike_times [1.0 2.0 3.0] >> SetStatus

Instructs the spike generator to generate events at 1.0, 2.0, and
3.0 milliseconds, relative to the device-timer origin.

Example:
Assume that NEST works with default resolution (step size) of 0.1ms
and default tic length of 0.001ms. Then, spikes times not falling
onto the grid will be handled as follows for different option settings:

/spike_generator << /spike_times [1.0 1.9999 3.0001] >> Create
---> spikes at steps 10 (==1.0ms), 20 (==2.0ms) and 30 (==3.0ms)

/spike_generator << /spike_times [1.0 1.05 3.0001] >> Create
---> error, spike time 1.05 not within tic/2 of step

/spike_generator << /spike_times [1.0 1.05 3.0001]
/allow_offgrid_times true >> Create
---> spikes at steps 10, 11 (mid-step time rounded up),
30 (time within tic/2 of step moved to step)

/spike_generator << /spike_times [1.0 1.05 3.0001]
/precise_times true >> Create
---> spikes at step 10, offset 0.0; step 11, offset -0.05;
step 31, offset -0.0999

Assume we have simulated 10.0ms and simulation times is thus 10.0 (step 100).
Then, any spike times set, at this time, must be later than step 100.

/spike_generator << /spike_times [10.0001] >> Create
---> spike time is within tic/2 of step 100, rounded down to 100 thus
not in the future, spike will not be emitted

/spike_generator << /spike_times [10.0001] /precise_times true >> Create
---> spike at step 101, offset -0.0999 is in the future

/spike_generator
<< /spike_times [10.0001 11.0001] /shift_now_spikes true >>
Create
---> spike at step 101, spike shifted into the future, and spike at step 110,
not shifted, since it is in the future anyways


Example:
spikegenerator
<< /spike_times [1.0 2.0] /spike_weights [5.0 -8.0] >>
SetStatus

Instructs the spike generator to generate an event with weight 5.0
at 1.0 ms, and an event with weight -8.0 at 2.0 ms, relative to
the device-timer origin.

spikegenerator << /spike_weights [] >> SetStatus

Instructs the spike generator to generate events at 1.0, 2.0, and
3.0 milliseconds, and use the weight of the connection.

Parameters:
 
The following properties can be set in the status dictionary.

origin double - Time origin for device timer in ms
start double - earliest possible time stamp of a spike to
be emitted in ms
stop double - earliest time stamp of a potential spike
event that is not emitted in ms
spike_times double array - spike-times in ms
spike_weights double array - corresponding spike-weights, the unit
depends on the receiver
spike_multiplicities int array - multiplicities of spikes, same length
as spike_times; mostly for debugging

precise_times bool - see above
allow_offgrid_spikes bool - see above
shift_now_spikes bool - see above

Sends:
SpikeEvent  

Author:
Gewaltig, Diesmann, Eppler  

SeeAlso: Source:
/home/nest/work/nest-2.14.0/models/spike_generator.h