       Re: How to Enable Automatic Recalculation

• To: mathgroup at smc.vnet.net
• Subject: [mg109860] Re: How to Enable Automatic Recalculation
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Wed, 19 May 2010 20:17:03 -0400 (EDT)

```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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