Given a list of 2-d points defining the vertices of a polygon, determine whether these points are sorted clockwise.

The inputs to this function are two vectors x and y (with equal size) containing the x- and y- coordinates of the polygon vertices, respectively.

The function should return true when sorted clockwise, and false when sorted counterclockwise (the polygon vertices will always be sorted either way).

Example:

x = [-1,-1,1,1];
y = [-1,1,1,-1];

defines a square, the vertices are listed clockwise

d_correct = true;