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Re: MatrixForm odd behaviour

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124491] Re: MatrixForm odd behaviour
  • From: roby <roby.nowak at gmail.com>
  • Date: Sat, 21 Jan 2012 05:19:03 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jf8q80$3iv$1@smc.vnet.net> <jfb3b0$hsm$1@smc.vnet.net>

Dear All.

One can argue a thousend times or even more that MatrixForm is for
display purpose only.
On the other hand the user majority (is this a democratic process ?)
would like to have the possibility to use MatrixForm or a similar
"Wrapper" in calculations.
The strange and funny thing is that matrices entered by <Insert><Table/
Matrix><New> provide a Form similar to MatrixForm which can be used in
calculations.
We just neeed a Wrapper for Display which should be ignored for
calculations, this would ease many things.
So the only thing we need is a simple way to apply the fuctionality
provided from matrix input menu to Mathematica matrix expressions, may be this
exists allready and I just missed soemthing ?

Cheers Robert


On 20 Jan., 07:58, "Oleksandr Rasputinov"
<oleksandr_rasputi... at hmamail.com> wrote:
> On Thu, 19 Jan 2012 10:11:12 -0000, roby <roby.no... at gmail.com> wrote:
> > Dear Group
>
> > As a similar Question is discussed on the group now.
>
> > The following issue:
>
> > When entering e.g.:
> > Dot[MatrixForm[{{1, 0}, {0, 2}}], MatrixForm[{{1, 0}, {0, 2}}]]
> > Mathematica does not evaluate the Dot operation and displays the two
> > unchanged
> > input matrices seperated by a "Dot" each respectively wrapped by
> > MatrixForm, so far so good (or perhaps not so good).
>
> > But if one now marks the most recent Mathematica output, the two "Dot"
> > seperated matrices and copy and paste's  them into a new Mathematica
> > cell,
> > both matrices still are seperated By "Dot", still looking like two
> > MatrixForm wrapped matrices.
> > But if you now evaluate the new cell guess what happens: the Dot
> > operation is performed (despite both matrices seem to be wrapped by
> > MatrixForm) and the result is displayed (of course not matrixForm
> > wrapped)
>
> > seems highly inconsistent, or ?
>
> > other funny things to try:
> > TraditionalForm[2] * TraditionalForm[2]
> > or:
> > Times[TraditionalForm[2], TraditionalForm[2]]
>
> > Cheers Robert
>
> Perhaps a bit obscure, but not (in my opinion) all that inconsistent when
> one understands how these things work.
>
> This behaviour comes about because the TagBox generated when MatrixForm is
> typeset for output is re-interpreted when given as input. However,
> MatrixForm does not get converted into a TagBox (unless this is done
> manually) except when it is typeset for output (the documentation usually
> contains phrases like "prints with..." for functions of this sort), so
> when given in an ordinary expression it stays where it is and can get in
> the way of operations on expressions wrapped with it. For example, doing
> the same thing manually:
>
> In :=
> boxes = ToBoxes@MatrixForm@IdentityMatrix[3]
>
> Out =
> < ugly box expression elided >
>
> In :=
> (* ToExpression interprets both strings and boxes *)
> ToExpression[boxes]
>
> Out =
> {{1, 0, 0}, {0, 1, 0}, {0, 0, 1}}
>
> One could perhaps argue that the statement in the documentation that
> "MatrixForm acts as a "wrapper", which affects printing, but not
> evaluation" is somewhat misleading as it is only true in a fairly narrow
> sense.




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