Fix incorrect dims in CompositeAffine [skip ci]

lib/matplotlib/tests/test_transforms.py

@@ -437,7 +437,6 @@ def test_rotate_around(self):
         assert_array_almost_equal(r90[2].transform(self.multiple_points), [
             [2, 2, 0], [-1, 0, 0], [2, 0, 4], [-3, 5, 0], [-4, 6, 6]])
 
-
         r_pi = [Affine3D().rotate_around(*self.pivot, np.pi, dim) for dim in range(3)]
         r180 = [Affine3D().rotate_deg_around(*self.pivot, 180, dim) for dim in range(3)]
 
@@ -448,7 +447,6 @@ def test_rotate_around(self):
         assert_array_almost_equal(r180[2].transform(self.multiple_points), [
             [0, 2, 0], [2, -1, 0], [2, 2, 4], [-3, -3, 0], [-4, -4, 6]])
 
-
         r_pi_3_2 = [Affine3D().rotate_around(*self.pivot, 3 * np.pi / 2, dim)
                     for dim in range(3)]
         r270 = [Affine3D().rotate_deg_around(*self.pivot, 270, dim) for dim in range(3)]
@@ -472,6 +470,16 @@ def test_rotate_around(self):
             assert_array_almost_equal(
                 (r90[dim] + r180[dim]).get_matrix(), r270[dim].get_matrix())
 
+    def test_scale(self):
+        sx = Affine3D().scale(3, 1, 1)
+        sy = Affine3D().scale(1, -2, 1)
+        sz = Affine3D().scale(1, 1, 4)
+        trans = Affine3D().scale(3, -2, 4)
+        assert_array_equal((sx + sy + sz).get_matrix(), trans.get_matrix())
+        assert_array_equal(trans.transform(self.single_point), [3, -2, 4])
+        assert_array_equal(trans.transform(self.multiple_points), [
+            [6, 0, 0], [0, -6, 0], [0, 0, 16], [15, -10, 0], [18, -12, 24]])
+
 
 def test_non_affine_caching():
     class AssertingNonAffineTransform(mtransforms.Transform):

lib/matplotlib/transforms.py

@@ -2833,10 +2833,8 @@ def __init__(self, a, b, **kwargs):
         if a.output_dims != b.input_dims:
             raise ValueError("The output dimension of 'a' must be equal to "
                              "the input dimensions of 'b'")
-        self.input_dims = a.input_dims
-        self.output_dims = b.output_dims
+        super().__init__(dims=a.output_dims, **kwargs)
 
-        super().__init__(**kwargs)
         self._a = a
         self._b = b
         self.set_children(a, b)