# equiv_sample_size , ftest

From: MICHAEL NOTARO (mnotaro AT XXXXXX)
Date: Wed Aug 20 2003 - 09:50:43 MDT

• Next message: Dennis Shea: "Re: equiv_sample_size"

I created variables sst1(lat,lon,time) and sst2(lat,lon,time),
and applied a low-pass filter to them. Then I calculated their
variances. For land pts. I use the FillValue of 1e+35.
Now, I want to determine if their variances are significantly
different using the ftest. I included my approach below.
However, the equiv_sample_size command leads to this error:

==>SLATEC/NCL: DGAMMA:
ANSWER LT HALF PRECISION BECAUSE X TOO NEAR NEGATIVE INTEGER: NERR=
1: LEVEL= 1
==>SLATEC/NCL: DBETAI: P AND/OR Q IS LE ZERO: NERR= 2: LEVEL=
2
==>SLATEC/NCL: DLBETA: BOTH ARGUMENTS MUST BE GT ZERO: NERR= 1
: LEVEL= 2
==>SLATEC/NCL: DGAMMA: X IS A NEGATIVE INTEGER: NERR= 4: LEVEL=
2

Previously, I did the same thing for surface air temperature without any errors.
Any idea what is wrong here? Thanks.
Mike

**********************

xEqv = equiv_
sample_size (sst1, 0.1,0)
yEqv = equiv_sample_size (sst2, 0.1,0)
gwt = latGauWgt (128, "lat", "gaussian weights", "dimension_less ")
xN = wgt_areaave (xEqv, gwt, 1., 0)
yN = wgt_areaave (yEqv, gwt, 1., 0)

alpha=new((/128,128/),float)
alpha = 100.*(1. - ftest(var1,xN,var2,yN,0))
alpha!0="lat"
alpha!1="lon"
alpha&lat=lat
alpha&lon=lon
alpha@_FillValue=1e+35