Re: Programmatically creating functions of many

*To*: mathgroup at smc.vnet.net*Subject*: [mg113670] Re: Programmatically creating functions of many*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sun, 7 Nov 2010 05:10:25 -0500 (EST)

Use SetDelayed rather than Set. Also, I recommend that instead of creating a list and applying Function to it, just use Function. graph = GraphData[ {"Grid", {2, 2}}, "AdjacencyMatrix"] // Normal; pairs = Position[graph, 1]; f := Function[{x}, And @@ Unequal @@@ Map[x[[#]] &, pairs, {2}]] f[{x1, x2, x3, x4}] x1 != x2 && x1 != x4 && x2 != x1 && x2 != x3 && x3 != x2 && x3 != x4 && x4 != x1 && x4 != x3 Note that this contains redundancies, e.g., both x1 != x2 and x2 != x1 Consequently, redefine pairs as pairs = Union[Position[graph, 1], SameTest -> (#1 == Reverse[#2] &)]; f[{x1, x2, x3, x4}] x1 != x2 && x1 != x4 && x2 != x3 && x3 != x4 Bob Hanlon ---- Yaroslav Bulatov <yaroslavvb at gmail.com> wrote: ============= Suppose I have a graph, and I'd like to create a function which checks whether given assignment of nodes is a proper labeling -- ie, no two adjacent nodes get the same number. One could do something like the following, but that gives Part warnings. Is there a preferred approach? graph = GraphData[{"Grid", {2, 2}}, "AdjacencyMatrix"] // Normal; f = Function @@ {{x}, And @@ (x[[First[#]]] != x[[Last[#]]] & /@ Position[graph, 1])} This is actually a problem that I periodically come across. Part approach causes warnings meanwhile something like Function @@ {Subscript[x,#]&/@Range[n], ...} doesn't work. What are typical ways of generating multivariate functions automatically? ---- Yaroslav http://stackoverflow.com/users/419116/yaroslav-bulatov