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MathGroup Archive 2007

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Re: Marking pivot elements in a matrix?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74939] Re: Marking pivot elements in a matrix?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 12 Apr 2007 04:48:20 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <evhuev$34o$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

and somthing like:

ShowPivotmark[matrix_?MatrixQ, index_] :=
   (RowBox[{"(", GridBox[matrix /. m_?MatrixQ :>
    ReplacePart[m,
         StyleBox[
           Part[matrix, Sequence @@ index],
           FontColor -> Red,
           FontWeight -> "Bold"], index],
           RowLines ->
                   Table[If[j == First[
                     index], True, False], {j,
                       Last[Dimensions[m]]}],
          ColumnLines ->
                     Table[If[i == Last[index],
                       True, False], {i, First[Dimensions[
                       m]]}]], ")"}] // DisplayForm)

with
m = Table[Random[Integer, {-2, 2}], {4}, {4}]

ShowPivotmark[m, {3, 2}]

does not help ??

Regards
   Jens

jackgold at umich.edu wrote:
> Hi folks,
> 
> I am writing notes for a class in which matrix manipulations
> is a necessary and frequent task. At present, when I wish to pick an 
> entry of the matrix as a "pivot" I simply write "pivot
> on {2, 3}". It would be nice to enclose the {2, 3} entry in a square or 
> circle to indicate it is the pivot entry. I am unable to do this. In 
> this same vein, I often have need to put a single vertical (horizontal) 
> line through the matrix.
> Mathematica provides the means for putting vertical (horizontal)
> lines in a matrix but it allows only the option of putting lines at 
> every column (row). I want to be more selective, say one line
> just before the last column. (This is the standard way of indicating
> that the last column is an augmentation to the original coefficient
> matrix).
> 
> Is there any reasonably simple way to do this?
> 


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