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Re: Using "=" vs ":="
*To*: mathgroup at smc.vnet.net
*Subject*: [mg70678] Re: Using "=" vs ":="
*From*: "Graham Michalk" <gmichalk at optushome.com.au>
*Date*: Mon, 23 Oct 2006 02:49:47 -0400 (EDT)
*References*: <ehf1ks$5ds$1@smc.vnet.net>
The arguments of all Functions in Mathematica must be enclosed by [ ... ]
not ( ... )
You should therefore have:
In[1]:= f[x_, y_]:=1-Sin[x^2+y^2]
Else what Mathematica does is to treat Sin(x^2+y^2) as the variable
Sin multiplied by the Expression (x^2+y^2), the latter evaluating to 5 for
x=1 and y=2
Sin 5 is equivalent to 5 Sin
Graham M
"misha" <iamisha1 at comcast.net> wrote in message
news:ehf1ks$5ds$1 at smc.vnet.net...
> 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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