Re: Gross Bug in Simplify

*To*: mathgroup at smc.vnet.net*Subject*: [mg32598] Re: [mg32585] Gross Bug in Simplify*From*: Andrzej Kozlowski <andrzej at platon.c.u-tokyo.ac.jp>*Date*: Thu, 31 Jan 2002 01:45:21 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

I can't see why you claim this is a bug and that it is caused by > Simplify misparses expressions m + n f[__], where m and n are > numeric, as (m+n) > f[__] It seems to me that what you are seeing is just a special case of the following: In[1]:= z/:z^v_=z; In[2]:= Simplify[1-z] Out[2]= 0 This seems to me entirely correct, since z==1 is the only complex number with the property that z^(anything)==z. Thus it would appear that your function f[z__] ought to have the value 1 for all arguments. This is consistent with all your outputs. Maybe I am missing your point, but mathematically at least there appears to be nothing wrong here. On Wednesday, January 30, 2002, at 05:19 PM, Alan Mason wrote: > There is a destructive bug in Mathematica (v4.1, win2000) in which > Simplify > misparses expressions m + n f[__], where m and n are numeric, as (m+n) > f[__]. One can only wonder how many other rule combinations, with or > without Simplify, are also faulty. > The following example is a stripped-down version of some rules for f = > Kronecker delta, which explains why the upvalue rule is needed. It is > specifically this rule that seems to be causing the problem with > Simplify. > However, it's not the upvalue itself -- the problem remains if Power is > Unprotected and the rule is replaced by Power[f[u__], v_] :> f[u]. > > In[1]:= > Clear[f]; > Simplify[1-f[4]] > f[u__]^v_ ^:= f[u]; > Simplify[{1-f[4], 1 - 7 f[4], 1 + f[4], 1 - x f[4]}] > > Out[2]= > 1-f[4] > > Out[4]= > {0,-6 f[4],2 f[4],1-x f[4]} > > Doesn't WRI test all its built-in functions by running special > diagnostic > code on them round the clock? It's hard to imagine how a bug like this > could have gone undetected! > > Alan > > > > Andrzej Kozlowski Toyama International University JAPAN http://platon.c.u-tokyo.ac.jp/andrzej/