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MathGroup Archive 1995

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Re:Re: re: automatic MatrixForm

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg799] Re:[mg744] Re: [mg698] re: automatic MatrixForm
  • From: Allan Hayes <hay at haystack.demon.co.uk>
  • Date: Wed, 19 Apr 1995 00:50:36 -0400

On Mon, 10 Apr 1995, Richard Mercer pointed out that MatrixForm  
will be used automatically on matrix outputs after entering the  
command

$PrePrint = If[MatrixQ[#],MatrixForm[#],#]&

It may be worthwhile to note that for MatrixQ[expr] to give True it  
is necessary not only that it be a list of lists of equal length  
but also that these latter lists contain no elements that are  
themselves lists.

Hence the following behaviour

In[1]:=
	$PrePrint = If[MatrixQ[#],MatrixForm[#],#]&;
In[2]:=
	{{1,2},{3,{4}}}
Out[2]=
	{{1, 2}, {3, {4}}}
But if we use
In[3]:=
	$PrePrint = If[TensorRank[#]===2,MatrixForm[#],#]&;
Then
In[4]:=
	mat
Out[4]=
	1     2

	3     {4}

Which you choose depends on what you want, and there are many variation.
It's also useful to note the options available for MatrixForm (the  
same as for TableForm).

Allan Hayes
hay at haystack.demon.co.uk


 


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