The "spikeinterval" object, submitted by Steve Nowlan, calculates interspike
intervals.  The input may be either continuous-valued action potentials from
a compartment, or true spikes, as produced by the "spike" or "random"
objects.  In the later case, this object is more robust than the
"freq_monitor" object, which can sometimes miss or double-count spikes which
last for only a single time step.  The "spikeinterval" object also allows
output of spike interval data to a file.

The Makefile included here uses the code in the subdirectory 'silib' to
produce a version of GENESIS called 'sgenesis'.  More detailed instructions
for compiling new objects into GENESIS may be found in the babel directory
'objects/testlib'.  The easiest way to try Steve's demonstration script
'SItest.g' is to carry out the following steps:

1)  Copy the files in this directory (including the subdirectory 'silib')
    into a directory of your own.

2)  If the file 'sgenesis' (provided on babel as a SUN SPARC executable)
    doesn't exist, or you are using a different machine, edit 'Makefile' to
    identify the MACHINE and XVERSION, as indicated by the comments in the
    file.  Give the command "make".  This will produce 'sgenesis'.

3)  Give the command "sgenesis", in order to run the new GENESIS.  Then give
    the command "include silib/silib" to make the new object known to
    GENESIS.

4)  The SItest script is set up to record spike intervals from '/cell1/soma'.
    As the "MultiCell" demo produces a compartment with this name, you may
    "cd /usr/genesis/Scripts/MultiCell" and type "MultiCell".  In order to
    make some space on the screen, iconify the "cell2" form.

5)  Now "cd" back to the directory where you have the 'spikeinterval' files,
    and give the command "include SItest".   A form with dialog boxes and
    a toggle button should pop up.

6)  Hit "return" in the first three dialog boxes so that the contents will be
    entered.  Change the contents of the "si_refract" box to "5".  This is
    because the default value provided (0.0015) is so small that it would
    count the finite width of the action potential as a spike at every time
    step.  Finally, toggle the bottom "toggle button" to "Saving".  (As
    explained in the documentation, this must be done after every RESET.)

7)  Now click on "STEP" in the MultiCell control form.

8) When the simulation has finished, use "more" to inspect the file
   'si.dat'. 

Alternatively, one could create a graph to record the spike intervals and
send a "PLOT interval" message from the si element to the graph, instead of
recording the data in a file.