Re: Using "=" vs ":="
- To: mathgroup at smc.vnet.net
- Subject: [mg70697] Re: Using "=" vs ":="
- From: Peter Pein <petsie at dordos.net>
- Date: Mon, 23 Oct 2006 02:51:08 -0400 (EDT)
- References: <firstname.lastname@example.org>
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:= f[x_, y_]:=1-Sin(x^2+y^2) > No problem so far... > Then, > In:= f[x,y] > Out:=1-Sin(x^2+y^2) > Still no problem... > Then, > In:=f[1,2] > Out:=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:= f[x_, y_]=1-Sin(x^2+y^2) > .... > In:=f[1,2] > Out:=1-Sin > > My question is, Why? What's the difference between ":=" and "=" for > defining functions? > > Thanks! > Misha > Hi Misha, try to use Mathematica syntax while using Mathematica. Sin is just a variable (multilyed by x²+y²) in your example. The second part of your posting is inconsistent: Out should be 1-5 Sin, if you entered f[x_,y_]=1-Sin(x²+y²) In:= f[x_,y_]:=1-Sin[x^2+y^2] (* "=" or ":=" doesn't matter in this case *) In:= f[1,2] Out= 1-Sin Peter P.S.: if you don't have access to brackets on your keyboard either buy a new one or use Sin@(x²+y²). ;-)