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What is happening here? (TagSet)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27866] What is happening here? (TagSet)
  • From: johntodd at fake.com (John Todd)
  • Date: Thu, 22 Mar 2001 04:30:07 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,
	I've been working my way through a notebook I found on the
Internet, and the author states the following before executing some
commands which I don't understand:

//begin copied text
There are two methods for defining a complex function in Mathematica.
Before we start, make x, y, u and v real variables.

Clear[u, v, x, y, z];
Clear[f, F, X, Y, U, V, Z];
TagSet[x, Im[x], 0];
TagSet[y, Im[y], 0];
TagSet[u, Im[u[x, y]], 0];
TagSet[v, Im[v[x, y]], 0];
TagSet[x, Re[x], x];
TagSet[y, Re[y], y];
TagSet[u, Re[u[x, y]], u[x, y]];
TagSet[v, Re[v[x, y]], v[x, y]];
//end copied text

I of course, understand the clear statements, but I can't figure out
what he's actually accomplishing.  I inserted statements akin to ?x,
?y, etc.  inbetween each instruction to see if anything was changing
and couldn't glean any information from that, then I wrapped a few of
the statements within a FullForm[] function call, which gave me
something similar to this:
//FullForm =
	0
which didn't help me at all.  I've looked at the documentation, the
Wolfram Book v.4 and searched the web, all to no avail.  I can't seem
to find what TagSet is doing.  I read through the section on
transformations and definitions as well, but there's nothing specific
that says TagSet[x1, x2,...xi] then explains how the arguments work
together.

Thanks for any and all illumination,

JT


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