Re: Baffling change to partial derivative in version 5.1

*To*: mathgroup at smc.vnet.net*Subject*: [mg61581] Re: Baffling change to partial derivative in version 5.1*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Sun, 23 Oct 2005 05:45:46 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <djcgvr$6n9$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Steven HANCOCK wrote: > Please, can anyone explain (or even just reproduce) the following behaviour? > > > In[1]:= > $Version > > Out[1]= > 5.1 for Microsoft Windows (October 25, 2004) > > In[2]:= > $ReleaseNumber > > Out[2]= > 0 > > In[3]:= > D[x y, t, NonConstants->{x}] > > Out[3]= > y D[x, t, NonConstants -> {x}] > > In[4]:= > D[x y, time, NonConstants->{x}] > > Out[4]= > 0 > > > Merely changing the spelling of the variable from t to time does not > return zero in version 4.2. > Thanks, Steve. > Hi Steve, I have the same weird behavior with Mathematica 5.2 on Windows XP. If we try to differentiate w.r.t. time1, time42, timtim, for instance, we still get 0. However, if we differentiate w.r.t. to tim or timetime, that works. Nevertheless, a variable called times yields 0 when a variable call Times yields the correct expression (see examples below). In[1]:= D[x*y, time, NonConstants -> {x}] Out[1]= 0 In[2]:= D[x*y, time1, NonConstants -> {x}] Out[2]= 0 In[3]:= D[x*y, time42, NonConstants -> {x}] Out[3]= 0 In[4]:= D[x*y, timetim, NonConstants -> {x}] Out[4]= 0 In[5]:= D[x*y, tim, NonConstants -> {x}] Out[5]= y*D[x, tim, NonConstants -> {x}] In[6]:= D[x*y, timetime, NonConstants -> {x}] Out[6]= y*D[x, timetime, NonConstants -> {x}] In[7]:= D[x*y, timetime, NonConstants -> {x}] Out[7]= y*D[x, timetime, NonConstants -> {x}] In[8]:= D[x*y, Times, NonConstants -> {x}] Out[8]= y*D[x, Times, NonConstants -> {x}] In[9]:= D[x*y, times, NonConstants -> {x}] Out[9]= 0 In[10]:= $Version Out[10]= "5.2 for Microsoft Windows (June 20, 2005)" Best regards, /J.M.