node voltage analysis
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werewolf
diyAudio Member

Join Date: Feb 2004
Location: Austin, TX
Quote:
 Originally Posted by MarcelvdG No simulator I know of can output a symbolic equation. Many can handle parameters and expressions with parameters, but you have to give all parameters a value before running the simulation and you get numerical values as output. By the way, when Alan Turing wrote down his system design for the ACE stored-program digital computer in late 1945, circuit simulation was already one of the applications he had in mind!
Thanks! That was my understanding (and memory), as well.

So, when I want to derive the frequency domain ("s" domain) input/output relationship of an RLC circuit, for example ... with non-numerical symbols (like R1, L3, C2) instead of specific values (1 kohm, 3 mH, 5 uF) ... i still do it by hand

pen and paper baby !!!

helitim
diyAudio Member

Join Date: Dec 2015
Location: Newfoundland
Quote:
 Originally Posted by werewolf So, when I want to derive the frequency domain ("s" domain) input/output relationship of an RLC circuit, for example ... with non-numerical symbols (like R1, L3, C2) ... pen and paper baby !!!
This is beyond my skill level. Every time I ask a question on this forum, I realize that I know less than previously thought. Eventually, I might realize that I know nothing!

rayma
diyAudio Member

Join Date: Apr 2011
Quote:
 Originally Posted by werewolf pen and paper baby !!!
Maple, and MATLAB with an added toolbox, can do symbolic math.
https://www.maplesoft.com/products/m...mericmath.aspx
Symbolic Math Toolbox - MATLAB

Ron E
diyAudio Member

Join Date: Jun 2002
Location: USA, MN
Quote:
 Originally Posted by MarcelvdG No simulator I know of can output a symbolic equation.
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you're welcome
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werewolf
diyAudio Member

Join Date: Feb 2004
Location: Austin, TX
Quote:
 Originally Posted by rayma Maple, and MATLAB with an added toolbox, can do symbolic math. https://www.maplesoft.com/products/m...mericmath.aspx Symbolic Math Toolbox - MATLAB
Quote:
 Originally Posted by Ron E SapWin Nuova pagina 1 you're welcome
are you guys trying to take away my pen and paper?

Seriously ... thanks for the links! Worth looking into

PRR
diyAudio Member

Join Date: Jun 2003
Location: Maine USA
Quote:
 Originally Posted by helitim ....do we just leave it up to spice?
The early SPICE papers are available online
here and
here.

They give some insight into how SPICE does it. However KCL and KVL (node analysis) are the key to ANY electrical calculation. Details differ: sometimes it is easier to work in conductances than resistances, etc. That's just flipping the fraction over.

The main difference between hand-calculation and SPICE is that a computer does math thousands of times faster than a human. So the computer may not set up a full analysis, it can just try-and-see. As I understand it, at some level of complexity, SPICE may assume the mid-point of a network is "half" the battery voltage. Then it computes all the currents and adds them up. By KCL they should sum to zero. They don't? Then SPICE adjusts its "half" guess, a little or a lot depending how far out it was, and does all the calculations again. In around a dozen to a hundred iterations it narrows-in on the "right" answer to 8 decimal places. (I may hand-calc 3 iterations to get 2 places, which is good enough for most work.)

Non-linear elements are represented by a formula which is recomputed for each iteration.

.TRAN analysis does all that many-many times over the specified time interval.

There's original FORTRAN SPICE, a C SPICE, and many folks who sell packages which include SPICE and typically with extra smarts (SPICE was put together quickly, so decades of smart programmers leads to little improvements).

Last edited by PRR; 21st November 2017 at 04:16 AM.

Dave Zan
diyAudio Member

Join Date: Nov 2010
Quote:
 Originally Posted by PRR The early SPICE papers are available online here and here.
Thank you for the links.
Always a fascination to read the primary sources.

Best wishes
David

 28th November 2017, 02:07 PM #18 gerhard   diyAudio Member     Join Date: Oct 2005 Location: near Stuttgart, south Germany In a previous life as a student, we had to program the underlying algorithms ourselves ( in isolation, not everyting together) for educational reasons b4 we were given access to spice. We used this book : < Computer Aided Network Design: Amazon.de: Donald Calahan: Fremdsprachige Bucher > and this one < Circuit Theory: A Computational Approach: Amazon.de: Stephen W. Director: Fremdsprachige Bucher > The second one contained an awful lot of typos and misprints, looks like Wiley could not afford a lector. :-( In concept, it was excellent, but unusable without a buglist. I bought that stuff in Nov. 76... __________________ "That's right!" shouted Vroomfondel, "we demand rigidly defined areas of doubt and uncertainty!" "We don't demand solid facts! What we demand is a total absence of solid facts. I demand that I may or may not be Vroomfondel!"

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