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RE: Re: Getting rid of the symbol -> after finding the root
*To*: mathgroup at smc.vnet.net
*Subject*: [mg39350] RE: [mg39326] Re: Getting rid of the symbol -> after finding the root
*From*: "David Park" <djmp at earthlink.net>
*Date*: Wed, 12 Feb 2003 03:52:38 -0500 (EST)
*Sender*: owner-wri-mathgroup at wolfram.com
Mostaghel,
Mathematica almost always returns the results of various "solving" routines
as a set of rules. Often there may be multiple variables and/or multiple
values and then you get sets of rules. You could save the rules and use them
later to substitute into some expression. Here is an example.
xsol = FindRoot[Cos[x] == x, {x, 1}]
{x -> 0.739085}
I saved the rule in the variable xsol. Then suppose you have an expression
in x. You can replace using xsol.
x^2 + 2x - 3
% /. xsol
-3 + 2*x + x^2
-0.975583
/. is the shortcut for ReplaceAll. (Lookup ReplaceAll in Help. Also lookup
Rule.) It uses the rule to replace each value of x.
Or you could replace x and save it once and for all.
Clear[x];
FindRoot[Cos[x] == x, {x, 1}]
x = x /. %
{x -> 0.739085}
0.739085
Now everytime you use x in an expression it will be replaced by its value.
x^2 + 2x - 3
-0.975583
I like the first procedure a little better because I don't like to assign
permanent values to a symbol like x.
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
From: Mostaghel, Naser [mailto:NMostag at UTNet.UToledo.Edu]
To: mathgroup at smc.vnet.net
Dear Friends,
I need to use the root of a simple equation in subsequent operations.
After extracting the root, it comes in the form ->root. I have not been
able to get rid of the symbol -> .
Can someone help?
Thanks,
Naser Mostaghel
Professor, Civil Engineering
T: (419) 530-8131
F: (419) 530-8116
E: nmostag at utnet.utoledo.edu
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