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Negative Variance? [message #65774]

Thu, 19 March 2009 15:00

anniebryant@gmail.com is currently offline

anniebryant@gmail.com
Messages: 16
Registered: March 2009

Junior Member

I am using the VARIANCE comand in IDL and am getting negative values.
The description in the HELP menu for IDL doesn't provide much
information, but from what I know, I thought variance was either an
absolute value or a deviation from a squared number, neither of which
could yield a negative value.

I am looking at the variance for 2 different bands in an AVIRIS
image. I use the same .pro, just change the band I am looking at.
The results for Band 1 (lets call it) make sense: all positive
values. For Band 2, I get a lot of negatives.?! How is this
possible.

These are the values for Band 1:

integer mean std dev minimum maximum n_elements
2633.3 2059.3 0.0000 9367.0 (160686) =
160686

These are the values for Band2:

integer mean std dev minimum maximum n_elements
1167.5 18269. -32768. 32767. (160686) =
160686

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Negative Variance?

By: anniebryant@gmail.com on Thu, 19 March 2009 15:00

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