A subgroup is some slice of a process array, formed by restricting the process coordinates in one or more dimensions to single values.
Suppose i is a location in a range distributed over a dimension of group p. The expression
p / i
represents a smaller group--the slice of p to which location i is mapped.
Similarly, a subrange is a section of a range, parameterized by a global index triplet. Logically, it represents a subset of the locations of the original range.
The syntax for a subrange expression is
x [ 1 : 49 ]
The symbol ``:'' is a special separator. It is used to
compose a triplet expression
, with optional int expressions to represent an
integer subset. The default initial and finial value are zero and the
extend of the range respectively. The default stride size is 1.