[R] Spreadsheet math problem (exponentiation)
Erich Neuwirth
erich.neuwirth at univie.ac.at
Fri Sep 18 18:06:23 CEST 2015
Methinks that any math teaching should make learners aware of the fact that
math conventions are not laws of nature, and that ambiguous expressions may
produce different values in different systems.
I think -2^2=4 is perfectly reasonable.
In my experience, most people after high school math do not know that
binary - und unary - are very different operations.
And that is the fault of the current way of teaching math!
> On Sep 18, 2015, at 18:00, John Kane <jrkrideau at inbox.com> wrote:
>
> A very good point re RExcel for sophisticated users. The majority of spreadsheet users, will never have heard of RExcel (or R for that matter) and very likely will no have the sophistication of knowing that they need to use brackets. Plus RExcel is not available in flavours for Apache OpenOffice or gnumeric as far as I am aware.
>
> If one actually learned the formal mathematical order of operations and still remembers them the expectation is that -2^2 will return -2. In a 20 sheet spreadsheet the error is likely to go completely undetected and may or may not have significant effect on final results.
>
> I, recently, was reading an education blog where the author was bemoaning the fact that shiny new math teachers were teaching that -2^2 = 4. Presumably they are putting their faith in Excel, etc., rather than the actual math conventions.
>
> John Kane
> Kingston ON Canada
>
>
>> -----Original Message-----
>> From: erich.neuwirth at univie.ac.at
>> Sent: Fri, 18 Sep 2015 17:13:44 +0200
>> To: r-help at r-project.org
>> Subject: Re: [R] Spreadsheet math problem (exponentiation)
>>
>> Let me add a little bit here:
>>
>> When using math formulas, one should know about the parsing rules form
>> complex expression
>> which do not have all the necessary parenthesis.
>>
>> Different systems do have different parings rules.
>> In the case of a^b^c, the expression is ambiguus because
>> (as mentioned in a previous mail) in general
>> (a^b)^c != a^(b^c)
>> To avoid unintended consequences, just us parentheses and you will get
>> the right result.
>> in the case of -a^b
>> The question is the order of precedence of unary - and binary ^.
>>
>> In Excel, -2^2=4, but 0-2^2=-4
>>
>> Reason: For Excel, unary - is stronger than the power operator, but
>> binary minus is weaker.
>>
>> My feeling is that too many people are bashing spreadsheets for the wrong
>> reason.
>> Spreadsheets ca do things R cannot do: Automatic recalculation when input
>> changes,
>> and visual point and click modelling of dependencies.
>> The calculation engine of Excel admittedly has some weak points.
>>
>> That is the reason why I wrote RExcel which gives you all the advantages
>> of the spreadsheet interface
>> and allows you to use the R calculation within this interface whenever
>> needed.
>
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