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Re: Baffling change to partial derivative in version 5.1


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.


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