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Re: MatrixForm affects values instead of only printing

  • To: mathgroup at smc.vnet.net
  • Subject: [mg100318] Re: [mg100298] MatrixForm affects values instead of only printing
  • From: "A. B." <functionalcoatings at gmail.com>
  • Date: Mon, 1 Jun 2009 07:05:48 -0400 (EDT)

The same holds for TableForm. I have already noticed this. It seems a bit
strange, given that "TableForm (MatrixForm) acts as a "wrapper", which
affects printing, but not evaluation."

In[194]:= list1 = {{1, 2, 3, 4}, {5, 6, 7, 8}}

Out[194]= {{1, 2, 3, 4}, {5, 6, 7, 8}}

In[195]:= Part[list1, All, 2]

Out[195]= {2, 6}

And...

In[196]:= list1 = {{1, 2, 3, 4}, {5, 6, 7, 8}} // TableForm

1    2    3    4
5    6    7    8


Part[list1, All, 2]

5
6
7
8


A.B.



> Here is the example:
> 
> test1={-3, 7, 5}
> test1[[3]]
> 
> returns the list and 5 as expected;
> 
> test2={-3, 7, 5}//MatrixForm
> test2[[3]]
> 
> returns a column vector and error: "part 3 of blah blah doesn't exist". The
> actual list itself is test2[[1]]. To get the right 3rd element I have to do:
> 
> test2[[1,3]]
> 
> which returns 5 as expected.
> 
> 
> The problem is MatrixForm is NOT supposed to change the expression it is
> applied on according to the manual. Is that a bug or there's logical
> explanation?
> 



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