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Re: The 'Solving a Block Diagram in Mathematica' web page

• To: mathgroup at smc.vnet.net
• Subject: [mg23590] Re: The 'Solving a Block Diagram in Mathematica' web page
• From: Eckhard Hennig <hennig at itwm.uni-kl.de>
• Date: Sun, 21 May 2000 18:12:56 -0400 (EDT)
• Organization: ITWM
• References: <8g7272$j49@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Peltio schrieb in Nachricht <8g7272$j49 at smc.vnet.net>...
>Just for the sake of knowing...
>Is the block diagram given at:
>
>http://library.wolfram.com/howtos/block/
>(Solving a Block Diagram in Mathematica)
>
>correct? I'm not an expert of control systems, but, shouldn't the two
>lower blocks be:
>
>(4s+2)/(s^2+2s+1) instead of 4s+2/(s^2+2s+1)
>(s^2+2)/(s^2+14) instead of s^2+2/(s^2+14)


Hi Peltio,

indeed, the diagram and the calculations do not match. But even with the
above corrections, the result appears to be incorrect. I computed the
transfer function of the block diagram with Analog Insydes, and the result
is slightly different:

http://www.itwm.uni-kl.de/as/products/ai/BlockDiagram.nb

(You can run these calculations with the evaluation version of Analog
Insydes.)

>Also, is there a particular convention that allows to understand which
>node is adding and which one is subtracting?
>Or am I missing something?


Unless an input to a summing junction is explicitly marked with a minus
sign, one can assume that the input is adding. But obviously, some minus
signs have been forgotten in the diagram.

Best regards,

  Eckhard

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Dr.-Ing. Eckhard Hennig        mailto:hennig at itwm.uni-kl.de
Institut fuer Techno- und Wirtschaftsmathematik e.V. (ITWM)
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     ITWM - Makers of Analog Insydes for Mathematica
        http://www.itwm.uni-kl.de/as/products/ai
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