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MathGroup Archive 2006

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Re: Using "=" vs ":=" [Thanks!]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70698] Re: Using "=" vs ":=" [Thanks!]
  • From: misha <iamisha1 at comcast.net>
  • Date: Mon, 23 Oct 2006 02:51:10 -0400 (EDT)
  • References: <ehf1ks$5ds$1@smc.vnet.net>

Thanks to all who responded.

Lesson 1: Caution for inexperienced users: Arguments of functions must 
be contained in brackets, "[...]", not parantheses, "(...)".  This is 
not mere notation!
Lesson 2: Set (=) vs. SetDelayed (:=) can be important.  I'm still 
trying to figure out when.  The examples in the help files and some of 
the responses have helped, but I'm trying to still trying to grasp the 
more general concept.

Thanks again!

Misha

misha wrote:
> I'm going through Mathematic by Example, 2nd ed., (Abell and Braselton), 
> and have come across something that puzzles me.
> 
> Chapter 2, Section 2, Example 8
> Define f(x,y)=1-sin(x^2+y^2)
> 
> So I first try,
> In[1]:= f[x_, y_]:=1-Sin(x^2+y^2)
> No problem so far...
> Then,
> In[2]:= f[x,y]
> Out[2]:=1-Sin(x^2+y^2)
> Still no problem...
> Then,
> In[3]:=f[1,2]
> Out[3]:=1-5 Sin
> 
> Huh?
> 
> I noticed that rather than using ":=" to "simply define" this function, 
> as opposed to (just) "=" to "define and compute" this function, I get 
> different subsequent behavior.  Specifically, doing the above with just 
> "=", works fine.
> In[1]:= f[x_, y_]=1-Sin(x^2+y^2)
> ....
> In[3]:=f[1,2]
> Out[3]:=1-Sin[5]
> 
> My question is, Why?  What's the difference between ":=" and "=" for 
> defining functions?
> 
> Thanks!
> Misha
> 


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