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More than three Independent Units equals death

Posted 11 years ago
Create three Quantities with Independent Units:
In[3]:= a1 = Quantity[2, IndependentUnit["aaa"]]
Out[3]= Quantity[2, IndependentUnit["aaa"]]
In[4]:= a2 = Quantity[3, IndependentUnit["bbb"]]
Out[4]= Quantity[3, IndependentUnit["bbb"]]
In[6]:= a3 = Quantity[4, IndependentUnit["ccc"]]
Out[6]= Quantity[4, IndependentUnit["ccc"]]
Add two of them, and you get an "incompatible units" warning, but it works (in the purrely formal sense, like a complex number, which is fine):
In[7]:= a1 + a2
During evaluation of In[7]:= Quantity::compat: IndependentUnit[aaa] and IndependentUnit[bbb] are incompatible units >>
Out[7]= Quantity[2, IndependentUnit["aaa"]] + Quantity[3, IndependentUnit["bbb"]]
Try adding all three, and it hangs:
In[8]:= a1 + a2 + a3
During evaluation of In[8]:= Quantity::compat: IndependentUnit[aaa] and IndependentUnit[bbb] are incompatible units >>
During evaluation of In[8]:= Quantity::compat: IndependentUnit[aaa] and IndependentUnit[bbb] are incompatible units >>
During evaluation of In[8]:= Quantity::compat: IndependentUnit[aaa] and IndependentUnit[bbb] are incompatible units >>
During evaluation of In[8]:= General::stop: Further output of Quantity::compat will be suppressed during this calculation. >>
Out[8]= $Aborted
A fair amount of instability seems to accompany using IndependentUnits...kernel crashing out of the blue.

Anyone understand this?
POSTED BY: Corey Mathers
2 Replies
It does not hang (Mma 9 on Windows 7 64 Bit), it reaches for some reason the $IterationLimit despite the fact that there is no iteration
 a1 = Quantity[2, IndependentUnit["a1"]];
 a2 = Quantity[3, IndependentUnit["a2"]];
 a3 = Quantity[4, IndependentUnit["a3"]];
 
 
 In[96]:= a1 + a2
 During evaluation of In[96]:= Quantity::compat: IndependentUnit[a1] and IndependentUnit[a2] are incompatible units >>
 Out[96]= Quantity[2, IndependentUnit["a1"]] + Quantity[3, IndependentUnit["a2"]]
 

In[100]:= a1 + a2 + a3 // Timing
During evaluation of In[100]:= Quantity::compat: IndependentUnit[a1] and IndependentUnit[a2] are incompatible units >>
During evaluation of In[100]:= Quantity::compat: IndependentUnit[a1] and IndependentUnit[a2] are incompatible units >>
During evaluation of In[100]:= Quantity::compat: IndependentUnit[a1] and IndependentUnit[a2] are incompatible units >>
During evaluation of In[100]:= General::stop: Further output of Quantity::compat will be suppressed during this calculation. >>
During evaluation of In[100]:= $IterationLimit::itlim: Iteration limit of 4096 exceeded. >>

Out[100]= {27.549777,
Hold[Quantity[4, IndependentUnit["a3"]] +
   Block[{$AutomaticUnitPlus = False},
    Message[Quantity::compat, IndependentUnit["a1"],
     IndependentUnit["a2"]];
    Quantity[2, IndependentUnit["a1"]] +
     Quantity[3, IndependentUnit["a2"]]]]}
and this takes you only 27 and a half second.
POSTED BY: Udo Krause
This hang happens in version 9.0.0.  It was fixed for 9.0.1.

$IterationLimit::itlim refers to an internal counter.
POSTED BY: Bruce Miller
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