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# r.regression.line

## man page of r.regression.line

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

```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=string   map2=string    [output=string]
[--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=string
Map for x coefficient

map2=string
Map for y coefficient

output=string
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), residuals (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 flag -s select the slower method (applies to FP  maps  only)  which
writes  out  all  pixel values individually to the temporary file.  The
results for offset/intercept (a) and gain/slope (b) are then  identical
to that obtained from R-stats's lm() function.

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

Last changed: \$Date: 2008-01-28 09:24:54 +0100 (Mon, 28 Jan 2008) \$

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(C) 2003-2010 GRASS Development Team

R.REGRESSION.LINE(1)
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