max(expr, dim1, dim2 <,tinc>)
Returns the maximum of expr over the specified 
dimension range. If the specified dimension is time, an
optional time increment tincr may be specified.
expr    - any valid GrADS expression dim1    - the starting dimension expressiondim2    - the ending dimension expressiontinc    - optional time increment
dim1 and dim2 are standard
GrADS dimension expressions whose dimensions must match.
maxloc, 
min, and
minloc. 
precip variable over the lon-lat domain, use nested max functions: 
d max(max(precip,lon=0,lon=360),lat=-90,lat=90)