Merge pull request #13 from rchristie/distance

Add magnitude/distance squared functions

Author: hsorby

src/cmlibs/maths/vectorops.py

@@ -13,6 +13,13 @@ def magnitude(v):
     return sqrt(sum(c * c for c in v))
 
 
+def magnitude_squared(v):
+    """
+    return: Squared scalar magnitude of vector v, avoiding sqrt().
+    """
+    return sum(c * c for c in v)
+
+
 def set_magnitude(v, mag):
     """
     return: Vector v with magnitude set to mag.
@@ -29,6 +36,32 @@ def sub(u, v):
     return [u_i - v_i for u_i, v_i in zip(u, v)]
 
 
+def distance(u, v):
+    """
+    :param u: Vector.
+    :param v: Vector.
+    :return: Scalar Euclidean distance between two points.
+    """
+    value = 0.0
+    for u_i, v_i in zip(u, v):
+        w = u_i - v_i
+        value += w * w
+    return sqrt(value)
+
+
+def distance_squared(u, v):
+    """
+    :param u: Vector.
+    :param v: Vector.
+    :return: Scalar squared Euclidean distance between points, avoiding sqrt().
+    """
+    value = 0.0
+    for u_i, v_i in zip(u, v):
+        w = u_i - v_i
+        value += w * w
+    return value
+
+
 def mult(v, s):
     """
     Calculate s * v

tests/test_vectorops.py

@@ -0,0 +1,30 @@
+import unittest
+from math import sqrt
+
+from cmlibs.maths.vectorops import distance, distance_squared, magnitude, magnitude_squared
+
+
+class VectorOpsTestCase(unittest.TestCase):
+
+    def test_magnitude(self):
+        v = [1.0, 2.0, -3.0]
+        expected_magnitude_squared = 14.0
+        expected_magnitude = sqrt(expected_magnitude_squared)
+
+        TOL = 1.0E-14
+        self.assertAlmostEqual(magnitude(v), expected_magnitude, delta=TOL)
+        self.assertAlmostEqual(magnitude_squared(v), expected_magnitude_squared, delta=TOL)
+
+    def test_distance(self):
+        u = [0.5, -0.1, 0.8]
+        v = [1.5, -2.1, 3.8]
+        expected_distance_squared = 14.0
+        expected_distance = sqrt(expected_distance_squared)
+
+        TOL = 1.0E-14
+        self.assertAlmostEqual(distance(u, v), expected_distance, delta=TOL)
+        self.assertAlmostEqual(distance_squared(u, v), expected_distance_squared, delta=TOL)
+
+
+if __name__ == "__main__":
+    unittest.main()