       Re: How to Enable Automatic Recalculation

• To: mathgroup at smc.vnet.net
• Subject: [mg109886] Re: How to Enable Automatic Recalculation
• From: "Nasser M. Abbasi" <nma at 12000.org>
• Date: Fri, 21 May 2010 06:45:23 -0400 (EDT)
• References: <ht1uua\$3cf\$1@smc.vnet.net>

```hi Murray;

I do not think using Dynamics is a good idea. For me Dynamics is like goto
on steroids, it makes it much harder to understand the logic of the code
when looking at the source code. (along the same lines of using goto's or
catch/throw to control logic of code would not be a good idea)

For me, I do not think Dynamics was a good thing to add to Mathematica. Yes,
it has cool side effects, but on the other hand, it makes programming in
Mathematica, when using Dynamics, so much more complex to understand.

We have the classic event listener GUI model around which everyone
understood how that works as it is a simple model why make a new one?  May
there is some good internal design reasons in Mathematica beyond my limited
understand of it which beyong the scope of this topic.

I now have a new measure of what makes a  Mathematica expert: You are a
mathematica expert, if you REALLY do understand Dynamics :)

--Nasser

"Murray Eisenberg" <murray at math.umass.edu> wrote in message
news:ht1uua\$3cf\$1 at smc.vnet.net...
> There IS a "simple" answer. Actually, two answers. it used to be that
> the only way to do this was to use SetDelayed ( := ) for the symbol you
> wanted to be recalculated whenever you changed another variable whose
> values was specified by Set ( = ).  Since Mathematica 6, you also have
> the more sophisticated method of using Dynamic quantities.
>
>    (* method 1: use SetDelayed instead of Set for b *)
>    a = 5;
>    b := 3 + a
>    b
> 8
>    a = Pi;
>    b
> 3 + Pi
>
>
>   (* method 2: use Dynamic *)
>   Clear[a,b]
>   Dynamic[a]
> a
>   a = 3;  (* preceding output changes to 3 *)
>   b = 3 + a
> 6
>   a = Pi;
>   b
> 3 + Pi
>
>   (* method 3: another way to use Dynamic *)
>   Clear[a,b]
>   a = 3;
>   Dynamic[b = 3 + a]
> 6
>   a = Pi;  (* preceding ouptput changes to 3 + Pi *)
>   b
> 3 + Pi
>
>
>
> On 5/19/2010 7:01 AM, Victor Roberts wrote:
>> I'm new to Mathematica, so perhaps there is a simple answer
>> to this question.
>>
>> How to I set Mathematica so that when I change the value
>> assigned to a variable it will automatically change all
>> later calculations that use that variable.
>>
>> For example, if I set
>>
>> a = 5
>>
>> and
>>
>> b = 3 + a
>>
>> I would like the value of b updated each time I change the
>> value of a.
>>
>> Right how, I need to recalculate each and every expression
>> that uses the variable a if I change its value.  There must
>> be a better way.
>>
>>
>> --
>> Vic Roberts
>> Replace xxx with vdr in e-mail address.
>>
>
> --
> Murray Eisenberg                     murray at math.umass.edu
> Mathematics & Statistics Dept.
> Lederle Graduate Research Tower      phone 413 549-1020 (H)
> University of Massachusetts                413 545-2859 (W)
> 710 North Pleasant Street            fax   413 545-1801
> Amherst, MA 01003-9305
>

```

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