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Re: A Use for Interpretation

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  • Subject: [mg85754] Re: A Use for Interpretation
  • From: David Bailey <dave at>
  • Date: Thu, 21 Feb 2008 17:57:20 -0500 (EST)
  • References: <> <fphcts$8ij$>

Murray Eisenberg wrote:
> Very nice!  Some other places where this might be employed are in laws 
> of exponents or laws of logs.  Or applying trig identities.  Or Laplace 
> transform.
> Ideally, this could be used not just by the teacher, but by the student 
> who would demonstrate that she knows the rules by "teaching them to the 
> computer".  Yet there's a "catch" to that: the Mathematica 
> sophistication needed, what with ReplaceRepeated, RuleDelayed, HoldForm, 
> ReleaseHold, and FreeQ.  Not to mention the "strange" definition of the 
> function, like "integrate" here, which must be defined in terms of itself.
> David Park wrote:
>> Since Version 6 appeared and I first encountered Interpretation I found it 
>> rather difficult to understand what use it might have. The examples in Help 
>> seem almost bizarre.
>> Here is one use where it works rather well. Teachers might often be 
>> frustrated in demonstrating the behavior of basic function such as D, 
>> Integrate or Limit because Mathematica automatically evaluates using its 
>> built-in rules. With Interpretation we can define a pseudo routine that 
>> displays as the real routine and then apply our own basic transformation 
>> rules. Here is an example with a linear breakout of Integrate.
>> integrate[integrand_, var_] :=
>>  Interpretation[HoldForm[Integrate[integrand, var]],
>>   integrate[integrand, var]]
>> We then define rules that breakout sums and constant factors. The rules even 
>> display in a nice form.
>> rule1 = integrate[a_ + b_, x_] -> integrate[a, x] + integrate[b, x]
>> rule2 = integrate[a_?(FreeQ[#, x] &) b_, x_] -> a integrate[b, x]
>> Then we can demonstrate how these rules work, performing the actual 
>> integration in the last step.
>> integrate[5 a Sin[x] + y Cos[x] + x^2, x]
>> % //. rule1
>> % //. rule2
>> % /. Interpretation[a_, b_] :> ReleaseHold[a]
I think there is a better way to do this. I use 
Inert[Integrate]Sin[x],{x,0,Pi}] and use a MakeBoxes rule to display the 
result as a grey-shaded integral. The advantage of this method is that 
it is possible to edit the contents of the inert integral and re-input 
the result.

David Bailey

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