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Re: statistics on large arrays [message #14680]

Wed, 24 March 1999 00:00

korpela
Messages: 59
Registered: September 1993

Member

In article <dcDJ2.929$Rd5.1323@news.flash.net>,
Steve Carothers <onav1@flash.net> wrote:
> Is there a limit to how large an array can be when finding the average or
> stdev of the entire array? I have an array of about 630,000 elements. When
> I try to find the average, the result is "NaNQ".

Are all of the values in the array defined values (i.e. not Inf or NaN)?
An Inf or a NaN in an array will cause the average to be NaN.

Eric

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Re: statistics on large arrays [message #14685 is a reply to message #14680]

Tue, 23 March 1999 00:00

Martin Schultz
Messages: 515
Registered: August 1997

Senior Member

Steve Carothers wrote:
>
> Is there a limit to how large an array can be when finding the average or
> stdev of the entire array? I have an array of about 630,000 elements. When
> I try to find the average, the result is "NaNQ".
>
> Steve

One thing you may want to try is to explicitely use a double formatted
array to overcome this problem (although you may then approach your
memory limits ...). Apparently, MEAN has a /DOUBLE keyword. Does it
help?

IDL> a=findgen(20)
IDL> print,mean(a) & help,mean(a)
% Compiled module: MEAN.
9.50000
<Expression> FLOAT = 9.50000
IDL> a=dindgen(20)
IDL> print,mean(a) & help,mean(a)
9.5000000
<Expression> DOUBLE = 9.5000000

Regards,
Martin.
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