Re: Help Mathematica - Generating Patterns

*To*: mathgroup at smc.vnet.net*Subject*: [mg54887] Re: [mg54852] Help Mathematica - Generating Patterns*From*: "David Park" <djmp at earthlink.net>*Date*: Sat, 5 Mar 2005 01:34:31 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Here are a couple of routines that I have in one of my packages. SymbolsToPatterns::usage = "SymbolsToPatterns[symbollist][expr] will convert symbols in expression, \ which are on symbollist, to named patterns."; SymbolsToPatterns[symbols : {_Symbol ..}][expr_] := expr /. Thread[symbols -> (Pattern[#, Blank[]] & /@ symbols)] LHSSymbolsToPatterns::usage = "LHSSymbolsToPatterns[symbollist][expr] will apply SymbolsToPatterns to \ the first part of expr."; LHSSymbolsToPatterns[symbollist_][expr_] := MapAt[SymbolsToPatterns[symbollist], expr, 1] {x1, x2, x3} % // SymbolsToPatterns[{x1, x2, x3}] {x1_, x2_, x3_} Often we may have derived an equation and then wish to use the equation as a substitution rule in subsequent derivations. That means we want to change the equation into a rule and specified symbols on the left hand side into patterns. Here is a trivial made-up example. (x + y)^2 == Expand[(x + y)^2] // Reverse rule = Rule @@ % // LHSSymbolsToPatterns[{x, y}] x^2 + 2*x*y + y^2 == (x + y)^2 (x_)^2 + 2*(x_)*(y_) + (y_)^2 -> (x + y)^2 David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Awgn78 [mailto:robynobile at gmail.com] To: mathgroup at smc.vnet.net How i can obtain a list {x1_,x2_,x3_} from a list {x1, x2, x3}... thank you for help and sorry for my bad english...i'm italian