MathGroup Archive 2005

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  • To: mathgroup at
  • Subject: [mg62567] MatrixForm
  • From: "David Park" <djmp at>
  • Date: Mon, 28 Nov 2005 00:57:59 -0500 (EST)
  • Sender: owner-wri-mathgroup at

Sometimes MatrixForm seems annoying because it is not transparent to other operations as some of the other Forms are. Actually, I think its design is very good because it allows one to write matrix equations with the Dot product in a nice form, and then easily evaluate them.

A = Array[a, {2, 2}];
B = Array[b, {2, 2}];

3 MatrixForm[A].MatrixForm[B]
% /. MatrixForm -> Identity // MatrixForm

The Dot product won't evaluate when the matrices are wrapped in MatrixForm and so we get the regular textbook form of a product. Notice also that the factor 3 was not sucked into the matrices. Using the rule  MatrixForm -> Identity then evaluates the matrix multiplication.

I don't know how many users are aware of this usage. I have just begun to appreciate it and thought I would post a note on it.

David Park
djmp at 

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