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matrix operations -- shared data vs copied

• To: mathgroup at smc.vnet.net
• Subject: [mg65917] matrix operations -- shared data vs copied
• From: robert.dodier at gmail.com
• Date: Sun, 23 Apr 2006 06:17:26 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

Hello,

I'm trying to get a handle on what Mathematica does with some
matrix operations. I wasn't able to figure it out by web or newsgroups
search so maybe you can help.

Suppose A is a matrix. Consider these operations.

(1) B = A

(2) myfunction[A]

(3) B = (some way of extracting column 1 of A)

(4) B = (some way of pasting A onto another matrix)

The question of interest is whether modifying elements of A also
modify B after operations (1), (3), and (4), and whether modifications
of the formal argument within myfunction also modify the actual
argument (namely A).

In some math languages, B = A and myfunction[A] actually create
copies of A, likewise row/column extraction and pasting matrices
together. But that's not the only way to do it; I'm trying to figure
out where Mathematica stands on this point.

Thanks for any pointers or other information.

Robert Dodier

• Follow-Ups:
  • Re: matrix operations -- shared data vs copied
    • From: Murray Eisenberg <murray@math.umass.edu>
  • Re: matrix operations -- shared data vs copied
    • From: "Szabolcs Horvát" <szhorvat@gmail.com>