Adding find_dependent_helpers

jitcxde_common/helpers.py

@@ -39,6 +39,26 @@ def filter_helpers(helpers,symbols):
 
 	return list(reversed(filtered_rev))
 
+def find_dependent_helpers(helpers,dependency):
+	"""
+	Returns a list of helpers depending on `dependency` and their respective derivative (applying the chain rule).
+	"""
+
+	dependent_helpers = []
+
+	for helper in helpers:
+		derivative = sum(
+				(
+					helper[1].diff(other_helper[0]) * other_helper[1]
+					for other_helper in dependent_helpers
+				),
+				helper[1].diff(dependency)
+			)
+		if derivative != 0:
+			dependent_helpers.append( (helper[0], derivative) )
+
+	return dependent_helpers
+
 def copy_helpers(helpers):
 	return [helper for helper in helpers]
 

tests/test_helpers.py

@@ -1,9 +1,9 @@
 #!/usr/bin/python3
 # -*- coding: utf-8 -*-
 
-from jitcxde_common.helpers import sort_helpers, filter_helpers, copy_helpers
+from jitcxde_common.helpers import sort_helpers, filter_helpers, copy_helpers, find_dependent_helpers
 import unittest
-from symengine import symbols
+from symengine import symbols, sin, cos, Integer
 from itertools import permutations
 
 p,q,r,s,u,v = symbols("p q r s u v")
@@ -39,6 +39,23 @@ def test_independence(self):
 		copy.append([u,v])
 		assert copy!=chain
 
+class FindDependentTest(unittest.TestCase):
+	def test_find_dependent_helpers(self):
+		helpers = [
+				( q, p           ),
+				( r, sin(q)      ),
+				( s, 3*p+r       ),
+				( u, Integer(42) ),
+			]
+		control = [
+				( q, 1        ),
+				( r, cos(q)   ),
+				( s, 3+cos(q) ),
+			]
+		dependent_helpers = find_dependent_helpers(helpers,p)
+		# This check is overly restrictive due to depending on the order and exact form of the result:
+		self.assertListEqual(dependent_helpers,control)
+
 if __name__ == "__main__":
 	unittest.main(buffer=True)