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MathGroup Archive 2006

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Re: Simple question from a biologist

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67166] Re: Simple question from a biologist
  • From: Peter Pein <petsie at dordos.net>
  • Date: Sun, 11 Jun 2006 02:17:43 -0400 (EDT)
  • References: <e6e27d$1tp$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

tnad schrieb:
> I'm a bit new to this so please bear with me. I solved this eqation:
> 
> Sol = Solve[{{{-x, 0, z}, {x, -y, 0}, {0, y, -z}}.{A, B, C} == 0, A + B + C == 1}, {A, B, C}]
> 
> and got the ouputs of A, B and C interms of x,y, and z each.
> 
> Now I want to express a term called "rate" where rate = Ax = By = Cz in terms of x, y and Z only.
> 
> So I tried to do this:
> Solve[rate == Ax , rate] /. Sol
> 
> but I cannot get the rate in terms of x,y and z.
> Is there a better way to do this? Also if someone knows of a better tuttorial (better than the built-in tuttorial) for mathematica, please let me know.
> 
You introduced a new variable Ax, but wanted A*x (or short: A x):

sol=Solve[{{{-x,0,z},{x,-y,0},{0,y,-z}}.{A,B,C}==0,A+B+C==1},{A,B,C}];

A x/.sol[[1]]
--> (x*y*z)/(x*y + x*z + y*z)

or if you insist on using Solve[] again:

Solve[rate==A x,rate]/.sol[[1]]
--> {{rate -> (x*y*z)/(x*y + x*z + y*z)}}

Peter


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