NAME

       r.regression.line  - Calculates linear regression from two raster maps: y = a + b*x.

KEYWORDS

       raster, statistics

SYNOPSIS

       r.regression.line
       r.regression.line help
       r.regression.line [-gs] map1=name map2=name  [output=name]   [--verbose]  [--quiet]

   Flags:
       -g
           Print in shell script style

       -s
           Slower but accurate (applies to FP maps only

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       map1=name
           Map for x coefficient

       map2=name
           Map for y coefficient

       output=name
           ASCII  file  for  storing  regression  coefficients  (output  to  screen  if  file not
           specified).

DESCRIPTION

       r.regression.line Calculates linear regression from two  raster  maps,  according  to  the
       formula  y  =  a  + b*x, where x and y represent raster maps.  Optionally saves regression
       coefficients  to  an  ASCII  file.   The  result  includes  the  following   coefficients:
       offset/intercept  (a)  and gain/slope (b), correlation coefficient (R), number of elements
       (N), means (medX, medY), standard deviations (sdX, sdY), and the F test  for  testing  the
       significance of the regression model as a whole (F).

NOTES

       The  results  for  offset/intercept  (a) and gain/slope (b) are identical to that obtained
       from R-stats's lm() function.

       The flag -s is inactive  as  always  high  precision  is  calculated  (kept  for  backward
       compatibility).

EXAMPLE

       Comparison of the old and the new DEM in Spearfish:
       g.region rast=elevation.10m -p
       r.regression.line map1=elevation.dem map2=elevation.10m

       Using the script style flag AND eval to make results available in the shell:
       g.region rast=elevation.10m -p
       eval `r.regression.line -g map1=elevation.dem map2=elevation.10m`
       echo $a
       479.615
       echo $b
       0.645631
       echo $R
       0.804441

AUTHOR

       Dr. Agustin Lobo - alobo at ija.csic.es
       Updated to GRASS 5.7 Michael Barton, Arizona State University
       Script style output Markus Neteler
       Conversion to C module Markus Metz

       Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $

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       © 2003-2013 GRASS Development Team