Let's take another look at the example of the array section in figure
4.2. We can capture this section
in a named variable as follows
In fact they are a different sort of range from any considered so
far--they are subranges. For completeness the HPJava language
provides a special syntax for constructing subranges directly.
Ranges equivalent to those of c can be created by
The global indices associated with the subrange , for example, are in the range . A subrange inherits locations from its parent range, but it specifically does not inherit global indices from the parent.
A non-trivial subrange is one for which the lower bound is not equal to zero, or the upper bound is not equal to , or the stride is not equal to 1.
A non-trivial subrange is never considered to have ghost extensions, even if its parent range does. This avoids various ambiguities that might otherwise crop up.
That covers the distributed ranges of sections.
What about the distribution groups of sections? Now
triplet subscripts don't cause problems--the distribution group
of c above can be defined to be the same as the distribution
group of the parent distributed array a. But the example of figure
4.1 is problematic. This was
constructed using a scalar subscript, effectively as follows: