Re: Getting rid of ProductLog
- To: mathgroup at smc.vnet.net
- Subject: [mg49258] Re: Getting rid of ProductLog
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Fri, 9 Jul 2004 02:26:37 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 7/8/04 at 2:51 AM, robert.hulme at gmail.com (Robert Hulme) wrote:
>Solve[a^b - b == c, b]
>Which gives me:
>Out[3]//TextForm=
> Log[a]
> ProductLog[-(------)]
> c
> a
>{{b -> -c - ---------------------}}
> Log[a]
>The problem with this is that I need the solution to use normal
>'primitive' (if thats the right word) math functions as I need the
>formula for a computer program.
>With ProductLog being an internal Mathematica function I cant
>therefore use this rearrangement.
>What can I do so that there is no ProductLog in there?
You can't. There is no closed form solution without the ProductLog function or the equivalent with a different name. If you are trying to write program that doesn't depend on Mathematica at runtime and need the solution to a^b - b == c, you will have to either write your own numeric solver or a routine to implement the ProductLog function.
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