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Re: copying a variable

  • To: mathgroup at smc.vnet.net
  • Subject: [mg92316] Re: copying a variable
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sat, 27 Sep 2008 22:19:20 -0400 (EDT)
  • References: <gbl303$m03$1@smc.vnet.net>

Hi,

if you call sub[] with sub[k]
k must be affected because
sub[k] expand to
With[{z=k},k[1]=4; k]

and when you return k from you sub[k] call r is set
to k and
r[1] -> k[1]

so that after
r=sub[k]

r[1] must return the same as k[1] because
r is set to k.

You can't have a copy of x because x is x, in the
best case you can copy the value of x but never x itself.

Regards
   Jens

ramiro wrote:
> Hello,
> This must be very simple.  Consider the following code:
> 
> k[1] = 2;
> sub[x_] := With[{z = x}, z[1] = 4; z]
> r = sub[k];
> r[1]
> k[1]
>  
> The output is
> 4
> 4
> 
> I would like to have the assignment inside the function (on z) don't 
> affect the parameter (x).  I would like to copy x so that whatever 
> assignment I do on z doesn't affect it, in other words, I would like to 
> return _a copy_ of x. So that the output should be:
> 
> 4
> 2
> 
> Thanks in advance,
> Ramiro
> 


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