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