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Re: mean() function [message #46957 is a reply to message #46935]

Sun, 15 January 2006 00:58

R.Bauer
Messages: 1424
Registered: November 1998

Senior Member

David Fanning wrote:

> biocpu@yahoo.com writes:
>
>> The following looks very odd. Have any clues?
>>
>> IDL> y = fltarr(1008879)+35
>> IDL> id = where(y ne 35, cc)
>> IDL> print, cc
>> 0
>> ; so y is strictly 35.0 BUT
>> IDL> print, mean(y)
>> 35.5249
>>
>> IDL> print, mean(y(0:400000))
>> 35.0000
>
> Goodness! It is the 10th already and this is the first
> "The Sky is Falling" post of the year. I was beginning
> to wonder what was going on! :-)
>
> You might want to have a look at this:
>
> http://www.dfanning.com/math_tips/sky_is_falling.html
>
> Cheers,
>
> David

mean is not useable if it results in this

IDL> print,mean( make_array(500000,val=35,/float) )
35.0413
IDL> print,mean( make_array(400000,val=35,/float) )
35.0000

I prefer a slower routine if this is right.

no one would accept 1.0 + 1.0 result = 1.5

The article is good to understand why mean should not be resolved this way!

Does one have implemented the gnu's version?

cheers
Reimar

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[Message index]

		Re: mean() function By: Maarten[1] on Thu, 12 January 2006 03:07
		Re: mean() function By: Paolo Grigis on Wed, 11 January 2006 06:19
		Re: mean() function By: Nigel Wade on Wed, 11 January 2006 01:49
		Re: mean() function By: Kenneth P. Bowman on Tue, 10 January 2006 19:22
		Re: mean() function By: biocpu on Tue, 10 January 2006 16:18
		Re: mean() function By: Paul Van Delst[1] on Tue, 10 January 2006 15:13
		Re: mean() function By: Paul Van Delst[1] on Tue, 10 January 2006 15:09
		Re: mean() function By: David Fanning on Tue, 10 January 2006 15:07
		Re: mean() function By: K. Bowman on Tue, 10 January 2006 15:00
		Re: mean() function By: Foldy Lajos on Tue, 10 January 2006 14:53
		Re: mean() function By: R.Bauer on Sun, 15 January 2006 00:58
		Re: mean() function By: savoie on Thu, 12 January 2006 08:49

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