       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[]
--> (x*y*z)/(x*y + x*z + y*z)

or if you insist on using Solve[] again:

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

Peter

```

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