RE: Rules

*To*: mathgroup at smc.vnet.net*Subject*: [mg66405] RE: [mg66359] Rules*From*: "David Park" <djmp at earthlink.net>*Date*: Thu, 11 May 2006 02:16:34 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

MR, There is no essential difference between the two. {rule1, rule2,...} simply allows you to apply more than one rule to the list. But what you should check is the difference between /. and //. (ReplaceAll and ReplaceRepeated). And you should carefully check the notes for ReplaceAll in Help. If AList has a value, then it will be evaluated before the rules are applied and therefore the rules will be applied to the items in AList. AList = {x, y, z}; AList /. x -> Sin[x] {Sin[x], y, z} If you write rule1 = AList -> BList giving {x, y, z} -> BList then AList /. rule1 BList but that would be a strange way of doing things. Basically the question is whether you want to give AList a value or not. If you want to use it symbolically in equations then it is better not to give it a value with a Set or SetDelayed statement. Rather, use a rule to substitute values when you are ready. Clear[AList] AListRule = AList -> {x,y,z} AList.{1, 2, 3}; % /. AListRule x + 2 y + 3 z David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Marcin Rak [mailto:umrakmm at cc.umanitoba.ca] To: mathgroup at smc.vnet.net Hey everyone, I had two simple questions, and was wondering wether anyone could through something my way: 1) When we have a list, call it AList, and we type the following AList /. {rule1} AList /. rule1 what is the difference between the two? And, how would I go about defining a rule for the variable AList, and a rule for the contents of the list - obviously these are two different concepts, yet how would you differentiate b/w the two? Thanx to all MR