[R] Spreadsheet math problem (exponentiation)
john.archie.mckown at gmail.com
Fri Sep 18 17:14:36 CEST 2015
On Fri, Sep 18, 2015 at 10:04 AM, David L Carlson <dcarlson at tamu.edu> wrote:
> Unfortunately the order of operations is not universal in computing. The
> real question is whether a program performs the way it is documented. Excel
> documents that unary operations take precedence over exponentiation and
> that within groups, the order is left to right. LibreOffice Calc behaves as
> Excel, but does not document the order of operations except to say */
> before +-, left to right. I couldn't find any statement about the order of
> operations in the documentation for Gnumeric.
> R documents that unary operations come after exponentiation and, within
> exponentiation, the order is right to left. Fortran puts unary operations
> with addition and subtraction after exponentiation with exponentiation
> right to left. C does not have an exponentiation operator, but unary
> operations come before multiplication and division.
> When in doubt, use parentheses to make sure you get what you want.
Very true. I do that if there is almost any chance that I, or another,
might not actually know which is first. I especially adopted this when I
learned a language called APL. It has _no_ precedence of operations. And it
does them from right to left. E.g. A=B*C+D is interpreted as A=B*(C+D). I
did programming in it for a couple of months. Then went back to normal
programming. Wrote completely _wrong_ code. When I asked a friend why the
calculation didn't get the "right" answer (2*4+3 == 14 was example I gave),
he looked at me like I was insane <grin/>.
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