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MathGroup Archive 2009

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Re: Usage of #1

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96294] Re: [mg96273] Usage of #1
  • From: "David Park" <djmpark at comcast.net>
  • Date: Wed, 11 Feb 2009 05:18:45 -0500 (EST)
  • References: <22848050.1234263649880.JavaMail.root@m02>

Nandhini,

The reason Mathematica returns a Root expression is that it is an EXACT
representation of a root of a polynomial equation. (Just as Pi and Sqrt[2]
are exact representations of the respective numbers.) Often, Mathematica can
do further combinations or simplifications and stay with the exact numbers.

#1 stands for the variable of the polynomial and 1+a #1+a^2 #1^5 & is a pure
function that represents the polynomial. Look up Function and Root in Help.
In this case the polynomial has a parameter, a. You can evaluate the Root to
an approximate number by replacing a with a number and then using N on the
expression. (% stands for the output of the previous line.)

Root[1+a #1+a^2 #1^5&,1]
%/.a->2
N[%]

giving

Root[1 + a #1 + a^2 #1^5 &, 1]
Root[1 + 2 #1 + 4 #1^5 &, 1]
-0.459175


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  


From: Nandhini [mailto:nandhini.gopalan at gmail.com] 

Frnds,
Im very new to mathematica. I have got a result where im getting
something like "Root[1+a #1+a^2 #1^5 &,1]. i wud like to know how else
i can write it. i dont want the #1 to b displayed. is tehre any
alternative. Plz help me out of this.

Thanks in advance,
Nandhini




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