spatial/barneshut: add Barnes-Hut force approximation package and R2/R3 helpers

spatial/r3/vector.go

@@ -0,0 +1,39 @@
+// Copyright ©2019 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package r3
+
+// Vec is a 3D vector.
+type Vec struct {
+	X, Y, Z float64
+}
+
+// Add returns the vector sum of p and q.
+func (p Vec) Add(q Vec) Vec {
+	p.X += q.X
+	p.Y += q.Y
+	p.Z += q.Z
+	return p
+}
+
+// Sub returns the vector sum of p and -q.
+func (p Vec) Sub(q Vec) Vec {
+	p.X -= q.X
+	p.Y -= q.Y
+	p.Z -= q.Z
+	return p
+}
+
+// Scale returns the vector p scaled by f.
+func (p Vec) Scale(f float64) Vec {
+	p.X *= f
+	p.Y *= f
+	p.Z *= f
+	return p
+}
+
+// Box is a 3D bounding box.
+type Box struct {
+	Min, Max Vec
+}