getPhase

  getPhase returns the phase of an event during a cycle

  Examples:
  phase=getPhase(trigchannel, eventchannel)
  phase=getPhase(trigchannel, eventchannel, start, stop)

  returns the phase of the events in eventchannel in relation to the cycles
  defined by the events in trigchannel

  If defined, start and stop give the time period to use. Otherwise these
  default to start=0 and stop=Inf.

  The output, phase, is a double precision vector. For each element, the
  fractional part represents the phase while the non-fractional part
  represents the number of the valid cycle that each event occurred
  in. Thus phase=2.75 indicates that an event occurred 3/4 of the way
  through the second valid cycle in the period start to stop.

  Only valid events in eventchannel will be used. For triggers, only
  valid events will be used to mark the start of a cycle but all physical 
  events will be searched for the end of cycle marker (i.e for the start
  of the subsequent cycle). This is useful when there are breaks in the
  data e.g. if there are 10 cycles but the 10th was interrupted, mark 1-9 as
  valid. Only these will be used for triggers but the onset of the
  interupted 10th cycle will be used to determine the length of the 9th
  cycle for calculating phase correctly.

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  Author: Malcolm Lidierth 08/08
  Copyright © The Author & King's College London 2008-
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