correlation_detector - Device for evaluating cross correlation between  
two spike sources
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
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.
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.

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
n_events integer vector - number of events from source
0 and 1. By setting n_events
to [0 0], the histogram is


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

/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 .]

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