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Re: Analog computer simulation in FORTH

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Richard Owlett <rowlett@pcnetinc.com> writes Re: Analog computer simulation in FORTH

> Fifty years ago analog computers were faster (i.e. shorter 
> turnaround time) than digital computers. Later digital computers 
> won out based on increased precision.

I remember being extremely frustrated about analog computers. 
Reason: having to scale one's algorithm made it completely unreadable.

It works well if the problem maps exactly on the analog hardware (i.e.
simulating an analog controller for an electrical problem).

> I've always had a bias towards analog computers. They were called 
> *ANALOG* computers for a reason. [For the youngsters, resistance, 
> capacitance, inductance, voltage and current were analogs of the 
> physical parameters of the system being simulated.]

But in the real world there are always discontinuities (opening/closing
a switch or valve, hitting a wall, putting your foot on the brake, 
controller saturation...)

Discretizing (w.r.t. time or amplitude) turns any linear problem into a
non-linear one.

> For the models I'm currently interested in SPICE or ECAP of the 
> 70's would be overly complex overkill. The versions I've had 
> contact with put much effort into transient analysis and 
> piecewise linear approximations of active devices.

With good reason, see the comments above.

> My world is much simpler.
> All passive components are linear and described by a positive scalar.
> My only active component is an ideal op-amp.
> When simulation begins, all inputs have been 0 since -infinity.

What is your point exactly? Do you want a simplified SPICE for your
problem, a SPICE written in Forth, or a simple SPICE to emulate a
Forth chip?

My NSPICE program is a simple SPICE written in Forth. It has a frontend which
only does DC analysis. It supports v/i controlled v/i sources and the usual
stuff.

> When doing a Google search I found
> http://code.google.com/p/propforth/downloads/detail?name=PropFacs.f.rtf

> It not suitable for me as it is targeted to a specific chip (I'll 
> be using a desktop machine.) and it appears not to be a standard 
> FORTH.

The designers and users are an odd bunch. I thought the chip was nice 
until I really looked at it -- the addressing modes are really 
inconvenient (no stacks). 

> It does show some work in FORTH exists.

> Pointers to further references?

What kind of work are you interested in? My SPIFSIM interfaces between
SPICE and Simulink. With NGSPICE one can write (interpreted!) device 
models in iForth, so components on your SPICE schematic can be Forth 
programs. Works well for emulating/simulating real-time digital control.

-marcel

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Analog computer simulation in FORTH Richard Owlett <rowlett@pcnetinc.com> - 2013-06-17 12:23 -0500
  Re: Analog computer simulation in FORTH mhx@iae.nl (Marcel Hendrix) - 2013-06-17 21:18 +0200
    Re: Analog computer simulation in FORTH Richard Owlett <rowlett@pcnetinc.com> - 2013-06-18 07:20 -0500
      Re: Analog computer simulation in FORTH m.a.m.hendrix@tue.nl - 2013-06-18 08:21 -0700
        Re: Analog computer simulation in FORTH Richard Owlett <rowlett@pcnetinc.com> - 2013-06-19 07:45 -0500

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