Investigate parallelism in the cyPackage

[WorkGitAccount]

The documentation written by Cem Yeksel in the C++ cyPackage has references to parallel options that are available but currently unused.

This will be a brief stretch goal to show proof of concept.

• [x] Investigate the cyPackage documentation and referenced parallel libraries.
• [ ] Add a write-up to the documentation. Add comments for future developers.

[WorkGitAccount]

• Parallel libraries only applies to cyPointCloud.h and are used when included.
• Can use Intel's TBB library or Microsoft's Parallel Patterns Library (PPL) by adding

  include "ppl.h"

  in cySampleElim.h prior to

  include "cyPointCloud.h"

• cyPoindCloud uses preprocessor directives to set macro _CY_PARALLEL_LIB to 'Concurrency' when pll.h is included.
• Then in BuildKDTree(), a preprocessor conditional checks if that macro is defined. If so, a test against a parallel_invoke_threshold (256). Only then call Concurrency::parallel_invoke( BuildKDTree(start,mid), BuildKDTree(mid+1,end) )
• When no parallel library is included, BuildKDTree() is called sequentially.
• Note that BuildKDTree is recursively built. It splits in half, then calls itself with each piece through the tree.
• Parallel invoke() takes a list of commands to run in parallel. So it's used to run the bisecting recursion in parallel down the tree up until the threshold is met (since at some threshold, sequential is faster).

[t:95]

[WorkGitAccount]

Following the previous comment, a PointCloud parallel option is implemented using #include "pll.h" in cySampleElim.h.

A threshold 256 suggests marginal speedups with smaller data sets. Can make the code edits for it to run in parallel, then do some sequential vs parallel timing analysis with large data sets.

[t:15]

[WorkGitAccount]

Tried to install both possible libraries TBB and PLL. Ran into issues.

[t:150]