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Re: MatrixForm affects values instead of only printing

  • To: mathgroup at smc.vnet.net
  • Subject: [mg100317] Re: [mg100298] MatrixForm affects values instead of only printing
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Mon, 1 Jun 2009 07:05:34 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

You included MatrixForm as part of the definition of test2

test2 = {-3, 7, 5} // MatrixForm

MatrixForm[{-3, 7, 5}]

?test2

Global`test2

test2=MatrixForm[{-3,7,5}]


You want MatrixForm applied to the output not the definition, i.e.,

(test2 = {-3, 7, 5}) // MatrixForm

MatrixForm[{-3, 7, 5}]

?test2

Global`test2

test2={-3,7,5}


test2[[3]]

5


Bob Hanlon

---- summer <summertan at hotmail.com> wrote: 

=============
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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