[GRASS-stats] new module for multiple regression with large raster maps

[Markus Metz]

There is a new module r.regression.multi as grass7 add-on to calculate
multiple regressions with raster maps. The motivation for this module
is to calculate regression coefficients and statistics for very large
datasets, too large for e.g. R. The module uses less than 3 MB memory
for 400 million cells with one response variable and 8 predictors.
Including residuals, this makes a total of 4 billion numbers.
Calculation takes about 4 minutes for this dataset on my laptop. In
addition to the slope estimates, statistics provided are R squared,
adjusted R squared, F, AIC, corrected AIC, BIC for the full model, and
F, AIC, corrected AIC, BIC for each predictor. Results are identical
to those produced by R (with smaller test datasets).

Markus M