Re: symbolic approximation (formular manipulation)

• To: mathgroup at smc.vnet.net
• Subject: [mg55018] Re: symbolic approximation (formular manipulation)
• From: dh <dh at metrohm.ch>
• Date: Thu, 10 Mar 2005 05:24:18 -0500 (EST)
• References: <d0mnef\$71b\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hello Zhe,
Try to formulate clearly what you want to do and the answer is obvious.
Because R1<<R2 you want to replace R1+R2 by R2
Because R2<<R3 you want to replace R2+R3 by R3
This can be done by ReplaceALL, abbreviated by /.

(R1+R2)/(R1(R2+R3))  /. {(R1+R2)->R2, R2+R3->R3}

have fun, Daniel

Zhe Hu wrote:
> A formula in electrical engineering can be simplified after assuming,
> e.g. R1<<R2, within 10% error tolerance.
>
> How this kind of "simplify" or approximation can be performed by Mathematica?
>
> For example, R1<<R2, R2<<R3
>
> R1+R2                      R2                                      R2
> ---------------  --->  ------------------  ---------> ------------------
> R1(R2+R3)               R1(R2+R3)                       R1 R3
>
>
>
> I thought about replacing: R1->0.00001*R2, but that would eliminate R1
> completely from the formula (denumerator), which is not favorable in
> some cases.
>

```

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