main/src/georegression/geometry/UtilPolygons2D_F64.java
public static void shiftDown( Polygon2D_F64 a ) {
		final int N = a.size();

		Point2D_F64 last = a.get(N-1);

		for (int i = N-1; i > 0; i-- ) {
			a.vertexes.data[i] = a.vertexes.data[i-1];
		}
		a.vertexes.data[0] = last;
	}
public static void shiftDown( Polygon2D_F64 a ) {
		final int N = a.size();

		Point2D_F64 last = a.get(N-1);

		for (int i = N-1; i > 0; i-- ) {
			a.vertexes.data[i] = a.vertexes.data[i-1];
		}
		a.vertexes.data[0] = last;
	}
Shifts all the vertexes in the polygon up one element.  Wraps around at the end
@param a Polygon