CUDA: Scatter communication pattern

Question

I am learning CUDA from the Udacity's course on parallel programming. In a quiz, they have a given a problem of sorting a pre-ranked variable(player's height). Since, it is a one-one correspondence between input and output array, should it not be a Map communication pattern instead of a Scatter?

Answer 1

CUDA makes no canonical definition of these terms, that I know of. Therefore my answer is merely a suggestion of how it might be or have been interpreted.

"Since, it is a one-one correspondence between input and output array"

This statement doesn't appear to be supported by the diagram, which shows gaps in the output array, which have no corresponding input point associated with them.

If a smaller set of values are distributed into a larger array (with resultant gaps in the output array, therefore, in which no input value corresponds to the gap location(s)), then a scatter might be used to describe that operation. Both scatters and maps have maps which describe where the input values go, but it might be that the instructor has defined scatter and map in such a way as to differentiate between these two cases, such as the following plausible definitions:

Scatter: one-to-one relationship from input to output (ie. unidirectional relationship). Every input location has a corresponding output location, but not every output location has a corresponding input location.

Map: one-to-one relationship between input and output (ie. bidirectional relationship). Every input location has a corresponding output location, and every output location has a corresponding input location.

Gather: one-to-one relationship from output to input (ie. unidirection relationship). Every output location has a corresponding input location, but not every input location has a corresponding output location.