[Date Index] [Thread Index] [Author Index]

Re: Re: Dynamic: feature?

• To: mathgroup at smc.vnet.net
• Subject: [mg88092] Re: [mg88068] Re: Dynamic: feature?
• From: John Fultz <jfultz at wolfram.com>
• Date: Thu, 24 Apr 2008 05:57:52 -0400 (EDT)
• Reply-to: jfultz at wolfram.com

On Wed, 23 Apr 2008 04:10:12 -0400 (EDT), Jean-Marc Gulliet wrote:
> Chris Osborn wrote:
>
>> I have a cell containing this:
>>
>> Dynamic[f[a, b]]
>>
>> Then I do this:
>>
>> a /: f[a, b] = 12
>>
>> and the dynamic cell updates to 12, as I would expect.
>>
>> When I do this:
>>
>> b /: f[a, b] = 45
>>
>> The dynamic cell does *not* update for some reason.
>> It seems as though it does not realize an update has occurred when it
>> is associated with b.
>>
>> Does anyone know why this is?
>>
>> Thanks in advance,
>> Chris
>>
> Weird. I witness the same behavior if the cells are evaluated in the
> given order. However, ff one change the order of the assignments (i.e. b
> first, then a) Dynamic[] works as expected. Evaluating the following
> expressions in that order,
>
> Dynamic[f[a, b]]
> (* The first output cell is: f[a, b] *)
>
> b /: f[a, b] = 45
> (* The first output cell is now: 45 *)
>
> a /: f[a, b] = 12
> (* The first output cell is now: 12 *)
>
> $Version => "6.0 for Mac OS X x86 (64-bit) (February 7, 2008)"
>
> I have also recorded the sessions in a PDF file. See
>
> http://homepages.nyu.edu/~jmg336/mathematica/weirddynamic.pdf
>
> Regards,
> -- Jean-Marc

A principle rule of debugging Dynamics...consider what Shift-Enter evaluations 
do.  In this case, exactly the same thing.  In fact, Dynamic correctly reflects 
what a Shift-Enter evaluation on f[a,b] would do at that very moment.

Sincerely,
 
John Fultz
jfultz at wolfram.com
User Interface Group
Wolfram Research, Inc.