       Re: simultaneous equations for chemical speciation

• To: mathgroup at smc.vnet.net
• Subject: [mg100214] Re: simultaneous equations for chemical speciation
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 28 May 2009 06:48:54 -0400 (EDT)
• Organization: Uni Leipzig
• References: <gvk9v0\$ono\$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de

```Hi,

and we can look on you post for ages, but we will never find out
*what* variables you wish to eliminate, so we will not found out *what*
error message or what's wrong.
And more over whe I try

eqn = {a == b + c + d, e == f + g + c + 2 d, h == c/(b*g),
i == d/(c*g), h*i == d/(b*g^2), j == m*g/f, k == l*m,
n + m + b + c == g + l}

syms = Cases[eqn, _Symbol, Infinity, Heads -> False] // Union

Eliminate[eqn, #] & /@ syms

all work fine with out an error message.

Regards
Jens

Jem & Tracy wrote:
> Hi, I am a postgrad student and completely new to mathematica, I am just
> starting to realise the possibilities.
>
> I am trying to do a chemical speciation calculation.
> I have a set of simultaneous equations which represents the equilibria,
> mass balance, and charge balance in the system.
>
> I want to eliminate some of the variables, and then be able to solve for
> the remaining ones.
> My system of equations looks like this:
> a=b+c+d
> e=f+g+c+2d
> h=c/(bg)
> i=d/(cg)
> hi=d/(bg^2)
> j=mg/f
> k=lm
> n+m+b+c=g+l
>
> Basically, I can solve for the variable I want, but I am having trouble
> eliminating the ones I don't want (ie. I am getting an answer that is in
> terms of the wrong variables)
> Sofar my formula looks like:
>
> Solve[{a == b + c + d, e == f + g + c + 2 d, h == c/(b*g),
>   i == d/(c*g), h*i == d/(b*g^2), j == m*g/f, k == l*m,
>   n + m + b + c == g + l}, {g}]
>
> If I use a similar formula for the "Eliminate" function, I get error
> mesages.
>
> I have been in the help files for ages, and don't really understand how
> to do this.
> I would really appreciate some pointers!!
> Thanks
>
>

```

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