On Fri, 29 Aug 2008, Jason Grout wrote:
>
> Jason Merrill wrote:
>> On Aug 29, 3:07 am, Burcin Erocal <[EMAIL PROTECTED]> wrote:
>>> On Thu, 28 Aug 2008 15:28:03 -0400
>>>
>>>
>>>
>>> Tim Lahey <[EMAIL PROTECTED]> wrote:
>>>> Hi,
>>>> Maple has a really useful feature of inert integrals
>>>> and derivatives. Basically, the integrals and derivatives
>>>> show up in the equations, but aren't evaluated until
>>>> a command to evaluate them is explicitly given. So,
>>>> you can delay the evaluation until after you've processed
>>>> the expression to the point where it can be evaluated.
>>>> This feature comes in very handy during complicated
>>>> derivations because you can see which terms are integrals
>>>> or derivatives and manipulate them along side
>>>> non-integrals/derivatives.
>>>> Is there a way to do this in Sage?
>>> This is not supported in Sage at the moment, but it is definitely
>>> planned. It should be fairly simple to implement this using the new
>>> symbolic function interface from ginac, which allows one to specify
>>> custom simplify/automatic evaluation functions.
>>>
>>> I am not familiar with the maple syntax. Can you give some examples of
>>> how to use these features so I can play with them without having to dig
>>> through documentation?
>>
>> The Mathematica syntax is Hold[Integral[x,{x,0,1}]]. This remains
>> unevaluated until it is wrapped with an Evaluate[]. The nice thing
>> about this syntax is that it works for any kind of expression (not
>> just integrals).
>
> So maybe we could have something like a FormalExpression class which
> does the same thing (has an argument that it doesn't evaluate).
Not sure how one would do this in Python though... (Maybe via preparsing
somehow, it would still be pretty hard...)
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