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Re: [Help-gnucap] Stochastic current inputs

From: a r
Subject: Re: [Help-gnucap] Stochastic current inputs
Date: Thu, 29 Nov 2007 23:13:46 +0000


What you're probably looking for is a monte-carlo analysis. I don't
know which free simulators implement it - you may have some luck with
Spice Opus. Otherwise go for hspice, spectre or some other commercial

You will need to add DC current sources to your network with current
values are defined by a single parameter. The parameter should be
defined by a random distribution (there are usually several predefined
distributions: uniform, gaussian etc.). Monte-carlo simulation first
sets all instances of used parameters accordingly to the selected
distribution and then runs the basic analysis (DC operating point in
your case). The whole process is repeated as many times as you want,
each time with new random values. So, what you get is a kind of a DC
OP analysis with a sweep.


On Nov 29, 2007 10:32 PM, Chinasaur <address@hidden> wrote:
> Hi, I'm new to gnucap, trying to use it to simulate the behavior of a network
> of biological cells.
> At the moment the only analyses I need to run are operating points.  The
> task is, given a network of cells with resistive connections between them,
> get the operating points under a series of stationary, stochastic input
> currents.
> In case that wasn't clear, here's one simple approach to the task.  I have
> one netlist with all the resistive elements.  I merge this with a netlist
> describing the independent current sources and then run the operating point,
> saving the output.  Then I stochastically generate a new current source
> netlist, merge the resistor netlist with the new current netlist, and run
> another operating point.  I repeat this several thousand times.
> Any advice on more sophisticated approaches to this problem?  I read through
> the documentation on behavioral modeling but didn't see any methods for
> designating stochastic current sources.  Are there SPICE variants with
> relevant functionality?
> Assuming I must implement this myself, any advice on optimization?  I
> thought the method described above was a bit inefficient since it involves
> reading in the resistive network over and over.  So I tried an
> implementation that at least avoids doing that.  I created a netlist
> describing the resistors and current sources, but using parameters to
> designate the current values.  Then I created a command file with .parameter
> commands for every current source followed by .op commands; this command
> file resets the current source parameters and runs the operating point over
> and over, up to 1000 times.  I thought this would be more efficient as it
> only loads the architecture of the resistive network once and then just
> overwrites the current source parameters each time.  But it seems there's
> some leak because the more times the parameters are reassigned, the slower
> everything runs.  Is this the behavior expected?
> Thanks in advance for any insight!
> P
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