[ferret_users] ferret inconsistency/errors in masking

[Lev Tarasov <lev@xxxxxx>]

I'm trying to merge some data sets, and get inconsistent
results:

For instance, variable hd, defined as follows:
yes?show var hd
 HD = IF IFLOAT GT 0.9 THEN H*(1.-0.91/1.028) ELSE HDG-SLEV
should equal hdg-slev for the following region, since ifloat=0:

yes? stats ifloat[g=h]
             IF H*0.91/1.028 LT SLEV+HP THEN 1 ELSE 0
             LONGITUDE: 89W (interpolated)
             LATITUDE: 36.5N (interpolated)
             Z:  N/A
             T: -121 to -33
             E:  N/A
             F:  N/A
             DATA SET: ./idHept.nn9894

 Total # of data points: 44 (1*1*1*44*1*1)
 # flagged as bad  data: 0
 Minimum value: 0
 Maximum value: 0
 Mean    value: 0 (unweighted average)
 Standard deviation: 0

but it doesn't:

yes? stats hd[g=h]-(hdg[g=h]-slev[g=h])

             HD[G=H]-(HDG[G=H]-SLEV[G=H])
             LONGITUDE: 89W (interpolated)
             LATITUDE: 36.5N (interpolated)
             Z:  N/A
             T: -121 to -33
             E:  N/A
             F:  N/A
             DATA SET: ./idHept.nn9894

 Total # of data points: 44 (1*1*1*44*1*1)
 # flagged as bad  data: 0
 Minimum value: -84.7
 Maximum value: 92.7
 Mean    value: -29.884 (unweighted average)
 Standard deviation: 46.089

 	FERRET v6.84
 	Linux 2.6.9-101.ELsmp 64-bit - 07/19/13

How do I fix this or is it a bug?

Cheers,

lev

Lev Tarasov -   Dept of Physics and Physical Oceanography,
		Memorial University of Newfoundland.
                email: lev@xxxxxx
                http://www.physics.mun.ca/~lev/
		Tel (709)-864-2675
		Fax (709)-864-8739