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Re: Replacement Rule with Sqrt in denominator

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  • Subject: [mg114520] Re: Replacement Rule with Sqrt in denominator
  • From: Bill Rowe <readnews at>
  • Date: Mon, 6 Dec 2010 06:14:21 -0500 (EST)

On 12/5/10 at 9:52 PM, fateman at (Richard Fateman)

>On 12/4/2010 3:14 AM, Bill Rowe wrote:

>>When an aspect of software works as designed it is inappropriate to
>>refer to that aspect as a bug.

>OK, I say "Dressing up a bug as a feature does not fix the bug."

And I agree.

>You say, in effect,

>If a designer writes a program that does exactly what the designer
>intended, then it is not a bug.


>OK, then, what term do you wish to use to refer to the result of
>design and programming that results from an error in the design

I don't agree the behavior of replacement rules reflects an
error in design.

>that causes mathematical computations to proceed in a way that is
>internally inconsistent, and is generally considered mathematical

Since replacement rules are not doing mathematics there should
be no requirement for the result to make mathematical sense.
That is a replacement rule such as 2->1 is perfectly valid but
clearly doesn't make 2 equal to 1.

>>The fact replacement rules operate on the FullForm of an expression
>>but what is displayed is not the FullForm does mean inexperienced
>>users of Mathematica will encounter some difficulties with
>>replacement rules. But, that simply doesn't equate to being a bug.

>No, I think the error is that users need to have another kind of
>pattern matching, and that when too many people stumble over the
>same feature, the correct response is NOT, "the customer is wrong,
>yet again."

>It might be ,  Oh, you want the semantic pattern matcher.
>Maybe, Here's how we can set it up to be your default command pattern

In another post Daniel Lichtblau described the issues with
trying to make replacement rules work on what is displayed
rather than full form.

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