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Update graham_scan_functions.hpp

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geometry/graham_scan_functions.hpp
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/******************************************************************************
* @file
* @brief Implementation of the [Convex
*Hull](https://en.wikipedia.org/wiki/Convex_hull) implementation using [Graham
*Scan](https://en.wikipedia.org/wiki/Graham_scan)
* Hull](https://en.wikipedia.org/wiki/Convex_hull) implementation using [Graham
* Scan](https://en.wikipedia.org/wiki/Graham_scan)
* @details
* In geometry, the convex hull or convex envelope or convex closure of a shape
* is the smallest convex set that contains it. The convex hull may be defined
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* points be sorting them with respect to the bottom-most point. Once the points
* are sorted, they form a simple closed path.
* The sorting criteria is to use the orientation to compare angles without
*actually computing them (See the compare() function below) because computation
*of actual angles would be inefficient since trigonometric functions are not
*simple to evaluate.
* actually computing them (See the compare() function below) because computation
* of actual angles would be inefficient since trigonometric functions are not
* simple to evaluate.
*
* Accept or Reject Points
* Once we have the closed path, the next step is to traverse the path and
* remove concave points on this path using orientation. The first two points in
* sorted array are always part of Convex Hull. For remaining points, we keep
*track of recent three points, and find the angle formed by them. Let the three
*points be prev(p), curr(c) and next(n). If orientation of these points
*(considering them in same order) is not counterclockwise, we discard c,
*otherwise we keep it.
* track of recent three points, and find the angle formed by them. Let the three
* points be prev(p), curr(c) and next(n). If orientation of these points
* (considering them in same order) is not counterclockwise, we discard c,
* otherwise we keep it.
*
* @author [Lajat Manekar](https://github.com/Lazeeez)
*