matrix - Square bracketed matrices in Mathematica

matrix - Square bracketed matrices in Mathematica - precision markers?

I'm trying to display Matrices with square brackets in Mathematica.

I've found this post from a mailing list in 2009 http://forums.wolfram.com/mathgroup/archive/2009/Aug/msg00458.html and it seems to work fine for whole numbers and symbols.

NotebookWrite[InputNotebook[], 
 TemplateBox[{GridBox[{{a, b}, {c, d}}]}, "Identity", 

  DisplayFunction -> (RowBox[{StyleBox["[", 
        SpanMaxSize -> \[Infinity]], #1, 
       StyleBox["]", SpanMaxSize -> \[Infinity]]}] &)]]

(* Outputs: *)
Identity[{
  {a, b},
  {c, d}
 }]


(* Which displays correctly as a square matrix. *)

But as soon as I try to input floating point numbers, I get floating point precision markers displayed. For example:

NotebookWrite[InputNotebook[], 
 TemplateBox[{GridBox[{{2.1, 1}, {1, 1.2}}]}, "Identity", 
  DisplayFunction -> (RowBox[{StyleBox["[", 
        SpanMaxSize -> \[Infinity]], #1, 
       StyleBox["]", SpanMaxSize -> \[Infinity]]}] &)]]

(* Outputs: *)

Identity[{
  {2.1000000000000001`, 1},
  {1, 1.2`}
 }]

(* Which displays correctly as a square matrix. *)

I don't see any function in there that would force the numbers to be evaluated into machine precision form. I think using HoldForm or others could solve this issue but I'm not too sure where that can be placed since GridBox needs a list and RowBox needs a box - evaluating them individually displays decimal numbers just fine.

For clarification, I'm looking for something like this:

(* In the square bracketed matrix display form of course *)

Identity[{
  {2.1, 1},
  {1, 1.2}
 }]

Any help for a beginner? Thank you!

Answer

makeBrackMat[mat_?MatrixQ] := 
     DisplayForm[
         RowBox[{StyleBox["[", SpanMaxSize -> \[Infinity]], 

                 GridBox[mat], 
                 StyleBox["]", SpanMaxSize -> \[Infinity]]}
         ]
     ];

Exact numbers:

mat1 = Partition[Range[12], 3];
makeBrackMat[mat1]

Machine-precision numbers:

mat2 = {{1.3, 2.9}, {9.5, 8.4}, {7.6, 0.2}};
makeBrackMat[mat2]

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