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Re: Solve question
*To*: mathgroup at smc.vnet.net
*Subject*: [mg57495] Re: Solve question
*From*: <wwolfe18 at comcast.net>
*Date*: Sun, 29 May 2005 21:00:12 -0400 (EDT)
*References*: <d79eqp$lcl$1@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
"Sterritt, Lanny" <lanny.sterritt at lmco.com> wrote in message
news:d79eqp$lcl$1 at smc.vnet.net...
> When the Solve command is used to obtain the value of a variable in an
> equation, something like {x -> value} is returned. How does one get
> Mathematica to automatically apply this value to following expressions
> in a notebook?
>
> L.W.Sterritt
For linear equations.
Here is one way:
Solve[2x == 6,x]
{x->3}
x=x/.%[[1]]
x now has the value 3.
To do this in one step:
x = Solve[2x == 6,x][[1,1,2]]
or
x = x/.Solve[2x == 6,x][[1]]
For equations with multiple roots picking out the root you want
automatically
is difficult. You may need to see all the roots before you assign one to x.
Solve[x^2==4,x]
{{x->-2},{x->2}}
x = x/.%[[1]]
This will set x equal to -2. Replace [[1]] with [[2]] to set x = 2.
Another approach is to name the output of Solve:
sol = Solve[x^2==4,x]
{{x->-2},{x->2}}
x = sol[[1,1,2] sets x = -2
x = sol[[2,1,2] sets x = 2
To do it all in one step:
x = Solve[x^2==4,x][[1,1,2] or x = Solve[x^2==4,x][[2,1,2]
I'm sure there are other ways to do this as well. Experiment with % and
Part.
Warren Wolfe
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