correlomatrix_detector – Device for measuring the covariance matrix from several inputs

Description

The correlomatrix_detector is a device that receives spikes from several pools of spike inputs and calculates the covariance matrix of inter-spike intervals (raw auto and cross correlation) binned to bins of duration delta_tau, which defaults to 5 times the simulation resolution. The histogram is only recorded for non-negative time lags. The negative part can be obtained by the symmetry of the covariance matrix :math:` C(t) = C^T(-t)`.

The result can be obtained from the node’s status dictionary under the key count_covariance.

In parallel it records a weighted histogram, where the connection weight are used to weight every count, which is available under the key /covariance. Both are matrices of size N_channels x N_channels, with each entry \(C_{ij}\) being a vector of size \(\tau_{max}/\delta_\tau + 1\) containing the (weighted) histogram for non-negative time lags.

The bins are centered around the time difference they represent, and are left-closed and right-open in the lower triangular part of the matrix. On the diagonal and in the upper triangular part the intervals are left-open and right-closed. This ensures proper counting of events at the border of bins, allowing consistent integration of a histogram over negative and positive time lags by stacking two parts of the histogram

\[(C(t)=[C[i][j][::-1],C[j][i][1:]]).\]

In this case one needs to exclude \(C[j][i][0]\) to avoid counting the zero-lag bin twice.

The correlomatrix_detector has a variable number of inputs which can be set via SetStatus under the key N_channels. All incoming connections to a specified receptor will be pooled.

Correlomatrix detectors ignore any connection delays.

Parameters

Tstart

real

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

real

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

ms

Bin width. This has to be an odd multiple of the resolution, to allow the symmetry between positive and negative time-lags. Defaults to 5 times the simulation resolution.

tau_max

ms

One-sided width. In the lower triagnular part events with differences in [0, tau_max+delta_tau/2) are counted. On the diagonal and in the upper triangular part events with differences in (0, tau_max+delta_tau/2]. Defaults to 10 times the value of delta_tau.

N_channels

integer

The number of pools. This defines the range of receptor_type. Default is 1. Setting N_channels clears count_covariance, covariance and n_events.

covariance

3D matrix of integers

matrix of read-only -raw, weighted, auto/cross correlation

count_covariance

3D matrix of integers

matrix of read-only -raw, auto/cross correlation counts

n_events

list of integers

number of events from all sources

Receives

SpikeEvent

See also

Device, Detector

Examples using this model

None