Q: How to generate a grid with sequential numbers?
In a shell, first get number of rows and columns as environment variables:
eval `g.region -g`
(or just note the output of g.region -p and insert the relevant value at the appropriate place in the formulas below)
Then use the variable 'rows' or 'cols' as follows:
r.mapcalc "grid_seq = col() * $rows + row() - $rows"
gives you a "vertical" sequence.
r.mapcalc "grid_seq = row() * $cols + col() - $cols"
gives you a "horizontal" sequence.