Re: Converting a number back to a symbol?

• To: mathgroup at smc.vnet.net
• Subject: [mg82904] Re: Converting a number back to a symbol?
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Sat, 3 Nov 2007 03:20:22 -0500 (EST)
• Organization: The Open University, Milton Keynes, UK
• References: <fgenct\$fsd\$1@smc.vnet.net>

```AES wrote:

<snip>

> But what about the reverse case: we have an expression containing
> various integer powers of Pi, and we want to replace all the explicitly
> appearing Pi's by 2 u0.  Writing
>
>    expr /. {Pi-> 2 u0}
>
> doesn't seem to do it.
>
> Is there a way?

Please, could you give a concrete example where such a transformation
does not work?

In[1]:= expr = Pi + Pi^2 + Pi^3 + (Pi/2 + (Pi/2)^2 + (Pi/5)^3) + 1/(Pi +
Pi^2 + Pi^3)

Out[1]=            2         3
3 Pi   5 Pi    126 Pi          1
---- + ----- + ------- + --------------
2       4       125            2     3
Pi + Pi  + Pi

In[2]:= expr /. Pi -> 2 u0

Out[2]=                       3
2   1008 u0             1
3 u0 + 5 u0  + -------- + --------------------
125                 2       3
2 u0 + 4 u0  + 8 u0

Regards,
--
Jean-Marc

```

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