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Re: Scalars Instead of Lists with One Element

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83526] Re: Scalars Instead of Lists with One Element
  • From: Gregory Lypny <gregory.lypny at videotron.ca>
  • Date: Thu, 22 Nov 2007 04:46:30 -0500 (EST)
  • References: <fhu75c$72j$1@smc.vnet.net> <4742F294.5050606@gmail.com>

Thanks everyone for your insights,

I've found the problem.  Say you want to sum a list whose elements are  
13 and 9.  Mathematica will return a list with one element, {22},  
rather than 22 if the original list is specified as a 2x1 column vector.

x = {{13}, {9}}; y = Total@x    >>> returns {22}

This also happens if you write x as I have above, or you use  
Mathematica's Insert menu to create a more visually appealing column  
vector, but it does not happen if you define x as a 2x1 array using  
the Array command.

I think it will happen with any matrix calculation whose result should  
otherwise be a scalar.  If we now let y be the row vector {1, 1} then

y.x    >>> returns {22}

The upshot of this is that any table that is created from calculations  
that make use of column vectors or matrix math will likely have a  
depth greater than 3, and you won't be able to cut and paste directly  
into a word processor or spreadsheet.

I'm going to have a look at some of the work-arounds that have been  
suggested in this thread and my related thread "Copy and Pasting  
Tables into Spreadsheet".


Gregory


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