RE: Re: Problem overriding simple built-in functions
- To: mathgroup at smc.vnet.net
- Subject: [mg28839] RE: [mg28800] Re: [mg28796] Problem overriding simple built-in functions
- From: "David Park" <djmp at earthlink.net>
- Date: Tue, 15 May 2001 00:59:12 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
But what possible benefit was there in the first place in making GCD listable? David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ > From: Andrzej Kozlowski [mailto:andrzej at tuins.ac.jp] To: mathgroup at smc.vnet.net > > The reason for all this is thet GCD has the Attribute Listable: > In[1]:= > Attributes[GCD] > > Out[1]= > {Flat,Listable,Orderless,Protected} > > This means that GCD[{2,3}] is just {GCD[2],GCD[3]} which is just {2,3}. In > order for your over-ride to work you will have to clear the Listable > attribute of GCD with ClearAttributes[GCD,Listable] . You will, of course, > loose all the benefits of listability. > > > -- > Andrzej Kozlowski > Toyama International University > JAPAN > > http://platon.c.u-tokyo.ac.jp/andrzej/ > http://sigma.tuins.ac.jp/~andrzej/ > > > > > on 01.5.13 4:28 PM, Jean-Christophe Deschamps at jchd at worldnet.fr wrote: > > > Hi, > > > > I'm told the following occurs under Mathematica v4.0: > > > > In[1]:= GCD[{3, 6}] > > Out[1]= {3, 6} > > In[2]:= GCD[x_List] := Apply[GCD, x] > > In[3]:= GCD[{3, 6}] > > Out[3]= GCD[{3, 6}] > > In[4]:= Apply[GCD, {3, 6}] > > Out[4]= 3 > > > > Why is it so? It looks like the override is ignored, but why? > > > > The same exerpt seems to work fine under version 2.x. > > > > > >