From b2137f2746ccbfabfffba98b60f6ed639322f1e8 Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Fri, 5 Jun 2020 13:21:35 -0700
Subject: [PATCH] Fixed z_to_vector for vectors on z-axis

---
 manimlib/utils/space_ops.py | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/manimlib/utils/space_ops.py b/manimlib/utils/space_ops.py
index 89124d47..c28c4224 100644
--- a/manimlib/utils/space_ops.py
+++ b/manimlib/utils/space_ops.py
@@ -137,11 +137,14 @@ def z_to_vector(vector):
     Returns some matrix in SO(3) which takes the z-axis to the
     (normalized) vector provided as an argument
     """
-    cp = cross(OUT, vector)
-    if get_norm(cp) == 0:
-        return np.identity(3)
+    axis = cross(OUT, vector)
+    if get_norm(axis) == 0:
+        if vector[2] > 0:
+            return np.identity(3)
+        else:
+            return rotation_matrix(PI, RIGHT)
     angle = np.arccos(np.dot(OUT, normalize(vector)))
-    return rotation_matrix(angle, axis=cp)
+    return rotation_matrix(angle, axis=axis)
 
 
 def angle_of_vector(vector):