## 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 00:24:54 -0800 (Mon, 28 Jan 2008) $*

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