GCD and LCM non-integer arguments

[Eike Rathke <erack@sun.com>]

Hi,

Section 6.14.33 GCD currently says:

| TODO: Applications differ on what happens when non-integers are
| provided. Excel 2003 always performs an INT() on each parameter first.
| OpenOffice.org 2.0.3 considers the full number, it computes GCD(1.1;2.2)
| as 1.1, and GCD(18.1;24.1) as 0. What if 0 returns?  OOO has a GCD and
| a GCD_ADD.   

OOo currently tries to calculate GCD and LCM with non-integer arguments,
more or less (more less) successfully. Btw, GCD(18.1;24.1) actually
returns 7.105427357601E-015 ...

Even if there may be applications to calculate a LCM of non-integers,
e.g. recurring period of overlapping wave forms, finding a corresponding
LCM/GCD pair that suffices the relation

|a*b| = GCD(a,b) * LCM(a,b)

with GCD really being the _greatest_ common divisor would probably go
beyond what we want to define here. I therefor propose to define that
arguments are to be converted to INT for both functions.

As for negative integer arguments: definitions of GCD say it is the
largest integer of the factorization and usually do not define that the
two numbers have to be positive integers or natural numbers, but speak
of integers. So negative arguments would be permittable, and as there
are always two possible solutions a and b for each GCD with a = -b, it
would also be correct to return a negative result if one of the
arguments is negative, as OOo currently does. However, most GCD
definitions say to ignore negative factorization, but it isn't required.
Anyway, negative arguments are perfectly valid, just that other
applications don't allow them. We could now define

a) If one of the arguments is negative, the function results in an
   error.

b) If exactly one of the arguments is negative the result is negative.
   If both arguments are negative the result is positive.

c) The result is always positive.

Opinions?


Btw, GCD(a;0) results in a. An additional definition allows GCD(0;0)==0,
which is useful and also is what Excel and Kspread do.

  Eike

-- 
Automatic string conversions considered dangerous. They are the GOTO statements
of spreadsheets.  --Robert Weir on the OpenDocument formula subcommittee's list.