Re: function composition
- To: mathgroup at smc.vnet.net
- Subject: [mg38187] Re: function composition
- From: "Francois Bernard Lauze" <francoisNO at SPAMit-c.dk>
- Date: Wed, 4 Dec 2002 03:26:32 -0500 (EST)
- Organization: UNI-C
- Sender: owner-wri-mathgroup at wolfram.com
"Tomas Garza" <tgarza01 at prodigy.net.mx> wrote in message news:ashulb$ejn$1 at smc.vnet.net... > Your first problem I don't understand. As for the second, this may give you > a taste of Mathematica's powers: > > In[1]:= > <<DiscreteMath`Combinatorica` > > In[2]:= > KSubsets[{a, b, c}, 2] /. {x_, y_} -> {x -> 0, y -> 0} > Out[2]= > {{a -> 0, b -> 0}, {a -> 0, c -> 0}, {b -> 0, c -> 0}} > Thanks for your answers! I find the KSubset beautiful! I realize that I was really too imprecise for the first problem. What i really want to do is to define some finite differences operators to discretize some PDE's. And for the composition pattern, it's meant to avoid involving points too far away when differentiating twice with respect with the same variable. So what I did was to define an explicit differentiation formula for that case and set, as indicated by the first answer, the HoldFirst attribute to my central difference operator. The problem with lists was in fact for extracting the coefficients of the discretization - the stencil. All in all it now works, and my code generates C routines. -- Francois Lauze The IT University of Copenhagen, Glentevej 67 2400 Kbh NV, Denmark Tel (45) 38 16 89 29