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MathGroup Archive 1999

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Re: Matrices-in-functions question

  • To: mathgroup at
  • Subject: [mg20486] Re: Matrices-in-functions question
  • From: "Stephen P Luttrell" <luttrell at>
  • Date: Wed, 27 Oct 1999 02:04:51 -0400
  • Organization: Defence Evaluation and Research Agency
  • References: <7v3c1t$>
  • Sender: owner-wri-mathgroup at

> Here is a simple one, but I can't work it out.
> I would like to be able to define a function this way:
> z=mat[[1]][[1]] a + mat[[1]][[2]]
> without specifying what "mat" is explicitly. I would evaluate it later
> way:
> z/.mat->somePredefinedMatrix
> Of course, Mathematica complains about the definition (Part specification
mat[[1]] is
> longer than depth of object) ... is there a way to make this fly?

I think this solves your problem:

z[mat_, a_] := mat[[1]][[1]] a + mat[[1]][[2]]

Use := rather than = to maintain the right hand side in unevaluated form
until the left hand side is actually used.

Stephen P Luttrell
Signal Processing and Imagery Department
DERA Malvern, St.Andrew's Road
Malvern, United Kingdom, WR14 3PS

+44 (0)1684 894046 (tel)
+44 (0)1684 894384 (fax)
luttrell at (email)

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