Re: Re: Problem overriding simple built-in functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg28848] Re: [mg28800] Re: [mg28796] Problem overriding simple built-in functions*From*: Andrzej Kozlowski <andrzej at tuins.ac.jp>*Date*: Tue, 15 May 2001 00:59:22 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

E.g.: In[5]:= GCD[{3,6,8,9},{6,4,6,12}] Out[5]= {3,2,2,3} It seems to me think this can be pretty useful. -- Andrzej Kozlowski Toyama International University JAPAN http://platon.c.u-tokyo.ac.jp/andrzej/ http://sigma.tuins.ac.jp/~andrzej/ on 01.5.15 2:44 AM, David Park at djmp at earthlink.net wrote: > 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. >>> >>> >> >> > >