Re: Automatic update of variables

*To*: mathgroup at smc.vnet.net*Subject*: [mg110327] Re: Automatic update of variables*From*: Erik Max Francis <max at alcyone.com>*Date*: Sun, 13 Jun 2010 04:12:02 -0400 (EDT)*References*: <huvk4q$rq0$1@smc.vnet.net>

Antonio De Ju=E1rez wrote: > Sometimes, I would find useful a method to update variables > automatically. For example, given the delayed rule > > b:=3 a+1; > > it would be useful to have b updated whenever a is assigned a new > value, like a=37. Is there any method to do this in Mathematica? I don't really follow the goal of what you're doing here. Using `:=` for assignment explicitly means that you do _not_ want the right-hand side of the expression evaluated. If `b` depends on `a` then the sensible thing to do here is to make `b` a function: b[a_] := 3 a + 1; and then do the appropriate substitute `b[somethingOrOther]` when the time is right. The only other thing I can think of that you might be trying to get at would be `Dynamic`, which you can look up. Perhaps if you said more about the problem you're trying to solve more generally, people could suggest a more appropriate solution. -- Erik Max Francis && max at alcyone.com && http://www.alcyone.com/max/ San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis War is like love, it always finds a way. -- Bertolt Brecht