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Re: Conversion Error? [message #16807 is a reply to message #16680]

Tue, 17 August 1999 00:00

m218003
Messages: 56
Registered: August 1999

Member

In article <4KVt3.65216$jl.41071979@newscontent-01.sprint.ca>,
"Laurent Chardon" <chardons@NOT_THISsprint.ca> writes:
> Thanks David and Martin for your help. So if I understand properly, IDL uses
> fix() by default when converting doubles to integer. That's tricky. Does it
> make sense to do that?
> The solution would be to use c=fltarr(round(size)). Shouldn't IDL do that by
> default?

Definitively NO! Most often you need truncation rather than rounding, e.g.
when you want to create an array with a certain number of elements. Of
course, you are right that in 99.9999999% of these circumstances,
99.9999999 should be interpreted as 100 and not 99, but that's how bits
work together ;-C Unfortunately, we are used to thinking decadal, whereas
practically every machine thinks dual (or for the convenience of the
programmer hexadecimal). You can open any book on digital numerics and you will
see how such roundoff errors are introduced. Unfortunately, you will not always
see lower values, else it would be easy enough to write
a = fltarr( long(expression) + 1 )

Martin

> I'm wondering what's the use of using fix() instead of round() in this
> instance. Does anybod know?
>
> Laurent Chardon
> Trent University
>
>

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[Message index]

		Conversion Error? By: Laurent Chardon on Mon, 16 August 1999 00:00
		Re: Conversion Error? By: m218003 on Tue, 17 August 1999 00:00
		Re: Conversion Error? By: steinhh on Tue, 17 August 1999 00:00
		Re: Conversion Error? By: Med Bennett on Mon, 16 August 1999 00:00
		Re: Conversion Error? By: davidf on Mon, 16 August 1999 00:00
		Re: Conversion Error? By: Laurent Chardon on Mon, 16 August 1999 00:00
		Re: Conversion Error? By: m218003 on Mon, 16 August 1999 00:00

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