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RE: Using "=" vs ":="
Misha, The problem is not '=' vs. ':='. The problem is Sin(x^2+y^2) vs. Sin[x^2+y^2]. The first form is not a function but just a multiplication. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: misha [mailto:iamisha1 at comcast.net] To: mathgroup 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:= 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