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Re: Commutativity of multiplication [message #50983 is a reply to message #50981]

Wed, 25 October 2006 14:54

Sven Geier
Messages: 17
Registered: July 2002

Junior Member

David Fanning wrote:
[...]
> It also explains this:
>
> IDL> f = 500L
> IDL> g = 1UL
> IDL> help, g*(-f)
> <Expression> ULONG = 4294966796
> IDL> help, (-f)*g

Wow. This is ... uhm ... "more interesting than I thought". There's whole
realms of oddity here that I never knew existed:

IDL> help,f,g
F LONG = -500
G ULONG = 1
IDL> print,f*g
-500
IDL> print,g*f
4294966796
IDL> if f*g eq g*f then print,f*g," equals ",g*f
-500 equals 4294966796

So for the sake of multiplication preservation of a sign is considered
important enough to break commutativity, but for the sake of comparison,
type conversion is performed that changes the value of an expression by
four billion.

Some days I can get all my exercise just by shaking my head over these kinds
of oddities...

Thanks for the reply, tho ...

- S

--
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[Message index]

		Re: Commutativity of multiplication By: JD Smith on Thu, 26 October 2006 10:47
		Re: Commutativity of multiplication By: JD Smith on Thu, 26 October 2006 10:37
		Re: Commutativity of multiplication By: Braedley on Thu, 26 October 2006 10:24
		Re: Commutativity of multiplication By: Foldy Lajos on Thu, 26 October 2006 01:26
		Re: Commutativity of multiplication By: JD Smith on Wed, 25 October 2006 16:09
		Re: Commutativity of multiplication By: David Fanning on Wed, 25 October 2006 15:33
		Re: Commutativity of multiplication By: Sven Geier on Wed, 25 October 2006 14:54
		Re: Commutativity of multiplication By: K. Bowman on Wed, 25 October 2006 13:42
		Re: Commutativity of multiplication By: David Fanning on Wed, 25 October 2006 13:54

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