# Command: correlation_detector

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Name:

    correlation_detector - Device for evaluating cross correlation between
      two spike sources

Description:

      The correlation_detector device is a recording device. It is used to record
      spikes from two pools of spike inputs and calculates the count_histogram of
      inter-spike intervals (raw cross correlation) binned to bins of duration
      delta_tau. The result can be obtained via GetStatus under the key
      /count_histogram.
      In parallel it records a weighted histogram, where the connection weights
      are used to weight every count. In order to minimize numerical errors the
      Kahan summation algorithm is used when calculating the weighted histogram.
      (http://en.wikipedia.org/wiki/Kahan_summation_algorithm)
      Both are arrays of 2*tau_max/delta_tau+1 values containing the histogram
      counts in the following way:

      Let t_{1,i} be the spike times of source 1,
      t_{2,j} the spike times of source 2.
      histogram[n] then contains the sum of products of the weight w_{1,i}*w_{2,j},
      count_histogram[n] contains 1 summed over all events with t_{2,j}-t_{1,i} in

      [ n*delta_tau	- tau_max	- delta_tau/2 , n*delta_tau	- tau_max + delta_tau/2 )

      The bins are centered around the time difference they represent, but are
      left-closed and right-open. This means that events with time difference
      -tau_max-delta_tau/2 are counted in the leftmost bin, but event with
      difference tau_max+delta_tau/2 are not counted at all.

      The correlation detector has two inputs, which are selected via the
      receptor_port of the incoming connection: All incoming connections with
      receptor_port = 0 will be pooled as the spike source 1, the ones with
      receptor_port = 1 will be used as spike source 2.

Parameters:

      Tstart	 double  	- Time when to start counting events. This time should
      be set to at least start + tau_max in order to avoid
      edge effects of the correlation counts.
      Tstop	 double  	- Time when to stop counting events. This time should be
      set to at most Tsim	- tau_max, where Tsim is the
      duration of simulation, in order to avoid edge effects
      of the correlation counts.
      delta_tau  double  	- bin width in ms
      tau_max   double  	- one-sided histogram width in ms. Events with
      differences in
      [-tau_max-delta_tau/2, tau_max+delta_tau/2)
      are counted.

      histogram	 double vector, read-only 	- raw, weighted cross
      correlation counts
      histogram_correction double_vector, read-only 	- correction factors for kahan
      summation algorithm
      count_histogram	 long vector, read-only  	- raw, cross correlation
      counts
      n_events	 integer vector		- number of events from source
      0 and 1. By setting n_events
      to [0 0], the histogram is
      cleared.

Receives:

    SpikeEvent

Remarks:

    This recorder does not record to file, screen or memory in the usual
      sense.

      Example:
      /s1 /spike_generator Create def
      /s2 /spike_generator Create def
      s1 << /spike_times [ 1.0 1.5 2.7 4.0 5.1 ] >> SetStatus
      s2 << /spike_times [ 0.9 1.8 2.1 2.3 3.5 3.8 4.9 ] >> SetStatus
      /cd /correlation_detector Create def
      cd << /delta_tau 0.5 /tau_max 2.5 >> SetStatus
      s1 cd << /receptor_type 0 >> Connect
      s2 cd << /receptor_type 1 >> Connect
      10 Simulate
      cd [/n_events] get ==   --> [# 5 7 #]
      cd [/histogram] get ==  --> [. 0 3 3 1 4 3 2 6 1 2 2 .]
      cd << /reset true >> SetStatus
      cd [/histogram] get ==  --> [. 0 0 0 0 0 0 0 0 0 0 0 .]

Availability:

    NEST

Author:

    Moritz Helias
      Jakob Jordan (implemented Kahan summation algorithm) 2013/02/18

FirstVersion:

    2007/5/21

SeeAlso:

- spike_detector
- Device
- PseudoRecordingDevice

Source:

    /opt/conda/conda-bld/nest_1512418773968/work/nest-2.14.0/models/correlation_detector.h

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