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MathGroup Archive 2007

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Re: Fuction definition

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73672] Re: [mg73635] Fuction definition
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sat, 24 Feb 2007 02:18:46 -0500 (EST)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <200702230942.EAA17911@smc.vnet.net>
  • Reply-to: murray at math.umass.edu

If you study the documentation about =: (SetDelayed) you will see that 
the expression on its right in p Sin[Pi x], for example, is evaluated 
not when you make the definition but rather when you subsequently 
evaluate an expression involving the left-hand side f2[x].

In your example, you don't ask for f1[0.5] until AFTER you have 
evaluated p = 2 (where = is Set).  Unless and until you change the value 
of p, it will keep the value of 2, and so evaluating f1[0.5] is the same 
thing as evaluating 2 Sin[Pi 2].



bar at ANTYSPAM.ap.krakow.pl.math.umass.edu wrote:
> Hi
> 
> When I try :
> ------------------
> p = 1;
> f1[x_] := p Sin[Pi x];
> p = 2;
> f2[x_] := p Sin[Pi x];
> 
> f1[0.5]
> f2[0.5]
> 
> Out[26]=2.
> 
> Out[27]=2.
> -----------------
> When I use = instead of := it works OK.
> Why ?
> 
> It is safely to use "=" in function definition ?
> 
> I have to integrate and differentiate such function in the future.
> In my case function depends on about 20 parameters, which are calculated
> three times, (I want to obtain three functions)
> 
> I'm not sure is this good idea to use '=' ?
> 
> Regards , Olaf
> 
> 
> 

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305


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