Re: NEWBIE: How do I use the results of a Solve?

*To*: mathgroup at smc.vnet.net*Subject*: [mg96016] Re: [mg95963] NEWBIE: How do I use the results of a Solve?*From*: "David Park" <djmpark at comcast.net>*Date*: Sun, 1 Feb 2009 04:41:50 -0500 (EST)*References*: <10148392.1233382822112.JavaMail.root@m02>

Tim, Here are a couple of step by step examples. Copy and paste each of the examples into a single cell in a Mathematica notebook and then evaluate. The Print statements give an annotation of the actions. The %% symbol refers to the piece of output from the second previous statement, that is it skips back over the Print output. The first example solves and equation for x and then substitutes the result into an expression: Print["Solve an equation"] Solve[x-12==0] Print["Take the first part of the first part. But you could get by with taking only the first part."] xsol=Part[%%,1,1] Print["This is the expression that you want to substitute in."] y== 5x Print["Perform the substitution"] %%/.xsol The second solution solves an equation with parameters for x and then uses the result to define a new function of the parameters. Print["Solve an equation with a parameters a and b for x"] Solve[a x-12+b==0,x] Print["Take the first part of the first part. But you could get by with taking only the first part."] xsol=Part[%%,1,1] Print["Define a function of x and substitute a and b"] f[a_,b_]=5 x/.xsol Print["Test the f function"] f[a1,b1] f[1,2] David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ From: Tim Heger [mailto:timheger at yahoo.com] I can't figure out how to use the results of Solve I just created as a new variable. Here's a simple example of what I am trying to do: Solve[some equation, x] Results in {x->12} I then want to use the x in y = x * 5 for example.... Obviously when I try to use this it fails because Mathematica sees the equation as y = {x->12} * 5 and not y = 12 *5 ... How do I change the results from the Solve from a rule to an actual value I can then use? Thanks, Tim