modelelgetsyn

  MODELELGETSYN - Return element number of synapses among particular neurons

   SYN_NUMS = MODELELGETSYN(MODELEL, PRELIST, POSTLIST)

   Return the model elements that correspond to synapses between elements
   PRELIST and POSTLIST.  SYN_NUMS(i) will be the synapse between 
   PRELIST(i) and POSTLIST(i), if they are both present and have a synapse.
   Otherwise, the SYN_NUMS(i) will be NaN;