This is part of the gridtools module

Setup a constant grid by either reading values from a file or definining a function in input

GRID_MIN	( default=auto ) the lower bounds for the grid
GRID_MAX	( default=auto ) the upper bounds for the grid
PERIODIC	are the grid directions periodic
FILE	the name of the file that contains the reference data
VALUE	the name of the value that should be read from the grid

FUNC	the function to compute on the grid
GRID_BIN	the number of bins for the grid
GRID_SPACING	the approximate grid spacing (to be used as an alternative or together with GRID_BIN)
VAR	the names to give each of the grid directions in the function. If you have up to three grid coordinates in your function you can use x, y and z to refer to them. Otherwise you must use this flag to give your variables names.