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node voltage analysis
node voltage analysis
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Old 20th November 2017, 10:13 PM   #11
werewolf is offline werewolf  United States
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Originally Posted by MarcelvdG View Post
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 !!!
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Old 20th November 2017, 10:26 PM   #12
helitim is offline helitim  Canada
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Originally Posted by werewolf View Post

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!
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Old 20th November 2017, 10:45 PM   #13
rayma is offline rayma  United States
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Originally Posted by werewolf View Post
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
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Old 20th November 2017, 11:08 PM   #14
Ron E is offline Ron E  United States
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Originally Posted by MarcelvdG View Post
No simulator I know of can output a symbolic equation.
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Old 21st November 2017, 12:56 AM   #15
werewolf is offline werewolf  United States
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Originally Posted by rayma View Post
Maple, and MATLAB with an added toolbox, can do symbolic math.
https://www.maplesoft.com/products/m...mericmath.aspx
Symbolic Math Toolbox - MATLAB
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are you guys trying to take away my pen and paper?

Seriously ... thanks for the links! Worth looking into
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Old 21st November 2017, 04:11 AM   #16
PRR is offline PRR  United States
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Originally Posted by helitim View Post
....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.
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Old 28th November 2017, 01:19 PM   #17
Dave Zan is online now Dave Zan  Australia
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Originally Posted by PRR View Post
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
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Old 28th November 2017, 02:07 PM   #18
gerhard is offline gerhard  Germany
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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...
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