Refs #28643 -- Added math database functions.

Thanks Nick Pope for much review.

tests/db_functions/math/test_atan2.py

@@ -0,0 +1,33 @@
+import math
+from decimal import Decimal
+
+from django.db.models.functions import ATan2
+from django.test import TestCase
+
+from ..models import DecimalModel, FloatModel, IntegerModel
+
+
+class ATan2Tests(TestCase):
+
+    def test_decimal(self):
+        DecimalModel.objects.create(n1=Decimal('-9.9'), n2=Decimal('4.6'))
+        obj = DecimalModel.objects.annotate(n_atan2=ATan2('n1', 'n2')).first()
+        self.assertIsInstance(obj.n_atan2, Decimal)
+        self.assertAlmostEqual(obj.n_atan2, Decimal(math.atan2(obj.n1, obj.n2)))
+
+    def test_float(self):
+        FloatModel.objects.create(f1=-25, f2=0.33)
+        obj = FloatModel.objects.annotate(f_atan2=ATan2('f1', 'f2')).first()
+        self.assertIsInstance(obj.f_atan2, float)
+        self.assertAlmostEqual(obj.f_atan2, math.atan2(obj.f1, obj.f2))
+
+    def test_integer(self):
+        IntegerModel.objects.create(small=0, normal=1, big=10)
+        obj = IntegerModel.objects.annotate(
+            atan2_sn=ATan2('small', 'normal'),
+            atan2_nb=ATan2('normal', 'big'),
+        ).first()
+        self.assertIsInstance(obj.atan2_sn, float)
+        self.assertIsInstance(obj.atan2_nb, float)
+        self.assertAlmostEqual(obj.atan2_sn, math.atan2(obj.small, obj.normal))
+        self.assertAlmostEqual(obj.atan2_nb, math.atan2(obj.normal, obj.big))