Merge pull request #1 from smichr/geom

test flyback removal in Polygon"

sympy/geometry/polygon.py

@@ -146,9 +146,12 @@ def __new__(cls, *args, **kwargs):
         i = -3
         while i < len(nodup) - 3 and len(nodup) > 2:
             a, b, c = nodup[i], nodup[i + 1], nodup[i + 2]
+            # if flyback lines are desired then the following should
+            # only be done if tuple(sorted((a, b, c))) == (a, b, c)
             if b not in shared and Point.is_collinear(a, b, c):
-                nodup[i] = a
                 nodup.pop(i + 1)
+                if a == c:
+                    nodup.pop(i)
             i += 1
 
         vertices = list(nodup)

sympy/geometry/tests/test_geometry.py

@@ -677,10 +677,14 @@ def test_ellipse_random_point():
 
 
 def test_polygon():
-    t = Triangle(Point(0, 0), Point(2, 0), Point(3, 3))
-    assert Polygon(Point(0, 0), Point(1, 0), Point(2, 0), Point(3, 3)) == t
-    assert Polygon(Point(1, 0), Point(2, 0), Point(3, 3), Point(0, 0)) == t
-    assert Polygon(Point(2, 0), Point(3, 3), Point(0, 0), Point(1, 0)) == t
+    a, b, c = Point(0, 0), Point(2, 0), Point(3, 3)
+    t = Triangle(a, b, c)
+    assert Polygon(a, Point(1, 0), b, c) == t
+    assert Polygon(Point(1, 0), b, c, a) == t
+    assert Polygon(b, c, a, Point(1, 0)) == t
+    # 2 "remove flyback" tests
+    assert Polygon(a, Point(3, 0), b, c) == t
+    assert Polygon(a, b, Point(3, -1), b, c) == t
 
     p1 = Polygon(
         Point(0, 0), Point(3, -1),