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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
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