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Re: Using "=" vs ":="

• To: mathgroup at smc.vnet.net
• Subject: [mg70690] Re: [mg70664] Using "=" vs ":="
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Mon, 23 Oct 2006 02:50:38 -0400 (EDT)
• Reply-to: hanlonr at cox.net

In either case, the definition of f should use square brackets for the Sin function. As shown in your output, you multiplied Sin times (x^2 + y^2)

Clear[f];
f[x_, y_]:=1-Sin[x^2+y^2];

f[1,2]

1 - Sin[5]

Look in the Help browser for Set (=) and SetDelayed (:=)


Bob Hanlon

---- misha <iamisha1 at comcast.net> 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
> 

--

Bob Hanlon
hanlonr at cox.net