[GRASS-dev] [grass-doc I][552] Comments upon the "r.regression.line" script.

grass-dev at lists.osgeo.org grass-dev at lists.osgeo.org
Tue Dec 4 21:04:36 EST 2007

doc I item #552, was opened at 2007-12-05 02:04
Status: Open
Priority: 3
Submitted By: Nikos Alexandris (nikosa)
Assigned to: Nobody (None)
Summary: Comments upon the "r.regression.line" script. 
Issue status: None
Doc section: raster
Doc timestamp (YYMMDD): 

Initial Comment:
Some comments upon the "r.regression.line" documentation (and script!)

(The formula of a regression line is, as given in the script is: y = a + b*x.)

(1) The terminology used in this script is a bit unconventional but makes more or less sense.
"a", which is the incept, is called offset and "b", which is the slope, is called gain.

(2) Among the results printed out after running the script (Line 105: echo "a  b  R  N  F medX  sdX  medY  sdY")

F is not explained anywhere.

Within the script (line 86) it is defined as F= R^2/(1-R^2/tot-2)

(3) Line 101 prints out: 

echo "   R: sumXY - sumX*sumY/tot"

which is actually half of the formula for Pearson's correlation coefficient "r" [ as correctly expressed in line 83: R= (sumXY - sumX*sumY/tot)/((sumsqX - sumX^2/tot)*(sumsqY - sumY^2/tot))^0.5 ]

(4) Line 103 prints out:

echo "   medX, medY: Medians"

allthough the "mean" is (correctly) used in the script (in lines 84 and 85, mediaX=sumX/tot and mediaY=sumY/tot respectively), it's incorrectly (?) named as "median".


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