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Q: implementation of Dot

  • To: mathgroup at
  • Subject: [mg7895] Q: implementation of Dot
  • From: Andreas Unterkircher <unterkir at>
  • Date: Thu, 17 Jul 1997 15:35:55 -0400
  • Organization: ETH Zuerich
  • Sender: owner-wri-mathgroup at

Hello !

I am puzzled about the following behaviour of the Mathematica (version
3.0) function "." (Dot):

In[1]= n = {{x},{y}};

In[2]= nn = {z};

In[3]= n . nn

Out[3]= {xz,yz}

Now I try

In[4]= m = {{},{}};
In[5]= mm = {};

In[6]= m . mm

Out[6]= {0}

I would have expected that either the operation m . mm (In[6]) is not
allowed at all or that Out[6] gives something like "{,}". I would
appreciate it very much if anybody can explain this behaviour to me. 


Andreas Unterkircher             Institut fuer Umformtechnik
ETH Zentrum / CLA, Tannenstr. 3,CH-8092 Zuerich, Switzerland
Phone: ++43 1 632 6621      

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