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# Bug 1777 - ft_spike_xcorr nlags/size of .xcorr field

Status | NEW |

Reported | 2012-10-10 14:42:00 +0200 |

Modified | 2015-07-15 13:06:30 +0200 |

Product: | FieldTrip |

Component: | spike |

Version: | unspecified |

Hardware: | PC |

Operating System: | Windows |

Importance: | P3 normal |

Assigned to: | Bart Gips |

URL: | |

Tags: | |

Depends on: | |

Blocks: | |

See also: |

## Bart Gips - 2012-10-10 14:42:12 +0200

Problem: ===================================== ft_spike_xcorr creates a stat.xcorr field of length cfg.maxlags*2, even though the help section says 2*maxlags+1. The 2*maxlags+1 makes sense: the result will give you -maxlag:maxlag, so maxlag lagging to maxlag leading. So changing line 198: s = zeros(nChans,nChans,2*nLags); to s = zeros(nChans,nChans,2*nLags+1); (together with the other changes needed) makes sense. ====================================== Secondly: A cross-correlation of two signals can only be of length equal to the sum of the lengths of the two signals minus 1. I.e. Signal A: 1 x M Signal B: 1 x N xcorr(A,B)= 1 x (M+N-1) So if the user would want a full xcorr the user should be able to select this. Right now this is not the case. This could be solved by either changing line 198 again: s = zeros(nChans,nChans,2*nLags-1); (but this would disregard the first point I made) or by adding a special case e.g. if nLags>length(spike.trial{n}) s = zeros(nChans,nChans,2*length(spike.trial{n})-1); end =========================================