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Re: simultaneous equations - eliminating variables and solving

  • To: mathgroup at smc.vnet.net
  • Subject: [mg100216] Re: simultaneous equations - eliminating variables and solving
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Thu, 28 May 2009 06:49:17 -0400 (EDT)
  • References: <gvlhv1$dq6$1@smc.vnet.net>

nninja 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
> 
> This is what my formula looks like sofar.
> 
> 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}]
> 
> 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)
> 
> 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
> 

Use the third argument to Solve.  See 
http://reference.wolfram.com/mathematica/ref/Solve.html

(But this particular set of equations doesn't seem to have a solution.)


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