Re: gEDA-user: Mathematical expressions in gnucap?

[al davis <ad151@xxxxxxxxxxxxxxxx>]

On Tuesday 18 September 2007, Peter Clifton wrote:
> Hi,
>
> I'm trying to use gnucap for simulating a machine - and am
> attempting to produce an electrically analogous sub-circuit
> circuit model to simulate the behaviour of a generator.
>
> I can get position and velocity (position is input from a
> sinusoidal source), and this is differentiated with a
> capacitor, and sensed with a CCVS.
>
> What I'm a little stuck on - is how I can use my arbitrary
> positions and velocities (which exist as terminal voltages)
> to feed an equation which determines the induced EMF on the
> generator coils.
>
> There needs to be a sin( position ) term as part of this.
>
> I believe ng-spice allows you to define functions, but
> couldn't "place" similar functionality in gnucap..

Spice has a "B" device that lets you define expressions.

It is planned for gnucap, high priority, but not done.  I have 
an expression evaluator.  Need to merge it in.

> Do I need to write my own model in C++?

There is nothing as easy as the "B" device.  Options available 
are 1. define as a poly, 2. use a table, 3. code a bm_ plugin 
in C++ (This really is easy.  Tell me what you want and I will 
show you.) 4. A more elaborate behavioral model as a .model 
file, which becomes a plug-in.


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