Matrix

Rakefile

@@ -3,7 +3,6 @@ require 'rake/testtask'
 
 desc 'Test'
 task :test do
-  sh 'jruby test/pbisector_test.rb'
   sh 'jruby test/circumcircle_test.rb'
   sh 'jruby test/triangle_points_test.rb'
 end

lib/math_demo/circumcircle.rb

@@ -1,5 +1,5 @@
 # Circumcircle from 3 points
-require_relative './pbisector'
+require 'matrix'
 
 class Circumcircle
   attr_reader :center, :radius, :points
@@ -8,29 +8,36 @@ def initialize(points)
   end
 
   def calculate
-    ab = PBisector.new(points[0], points[1]) # find 2 midpoints
-    bc = PBisector.new(points[1], points[2])
-    @center = circumcenter(ab, bc)
+    @center = Vec2D.new(-(bx / am), -(by / am))
     @radius = center.dist(points[2]) # points[2] = c
   end
 
   private
 
-  Vect = Struct.new(:x, :y, :z)
+  # Matrix math see matrix_math.md and in detail
+  # http://mathworld.wolfram.com/Circumcircle.html
 
-  def circumcenter(pb1, pb2)
-    # equation of the first bisector (ax - y =  -b)
-    a0 = Math.tan pb1.angle
-    v0 = pb1.midpoint
-    a1 = Math.tan pb2.angle
-    v1 = pb2.midpoint
-    eq0 = Vect.new(a0, -1, -1 * (v0.y - v0.x * a0))
-    eq1 = Vect.new(a1, -1, -1 * (v1.y - v1.x * a1))
-    # calculate x and y coordinates of the circumcenter
-    ox = (eq1.y * eq0.z - eq0.y * eq1.z) /
-         (eq0.x * eq1.y - eq1.x * eq0.y)
-    oy = (eq0.x * eq1.z - eq1.x * eq0.z) /
-         (eq0.x * eq1.y - eq1.x * eq0.y)
-    Vec2D.new(ox, oy)
+  def am
+    2 * Matrix[
+      [points[0].x, points[0].y, 1],
+      [points[1].x, points[1].y, 1],
+      [points[2].x, points[2].y, 1]
+    ].determinant
+  end
+
+  def bx
+    -Matrix[
+      [points[0].x * points[0].x + points[0].y * points[0].y, points[0].y, 1],
+      [points[1].x * points[1].x + points[1].y * points[1].y, points[1].y, 1],
+      [points[2].x * points[2].x + points[2].y * points[2].y, points[2].y, 1]
+    ].determinant
+  end
+
+  def by
+    Matrix[
+      [points[0].x * points[0].x + points[0].y * points[0].y, points[0].x, 1],
+      [points[1].x * points[1].x + points[1].y * points[1].y, points[1].x, 1],
+      [points[2].x * points[2].x + points[2].y * points[2].y, points[2].x, 1]
+    ].determinant
   end
 end

lib/math_demo/matrix_math.md

@@ -0,0 +1,17 @@
+### Matrix Math ###
+
+For detailed workings see [Circumcircle at Mathworld Wolfram.com][circumcircle]
+
+
+a = {{x<sub>1</sub> y<sub>1</sub> 1}, {x<sub>2</sub> y<sub>2</sub> 1}, {x<sub>3</sub> y<sub>3</sub> 1}}
+
+bx = -{{x<sub>1</sub><sup>2</sup> + y<sub>1</sub><sup>2</sup> y<sub>1</sub> 1}, {x<sub>2</sub><sup>2</sup> + y<sub>2</sub><sup>2</sup> y<sub>2</sub> 1}, {x<sub>3</sub><sup>2</sup> + y<sub>3</sub><sup>2</sup> y<sub>3</sub> 1}}
+
+by = {{x<sub>1</sub><sup>2</sup> + y<sub>1</sub><sup>2</sup> x<sub>1</sub> 1}, {x<sub>2</sub><sup>2</sup> + y<sub>2</sub><sup>2</sup> x<sub>2</sub> 1}, {x<sub>3</sub><sup>2</sup> + y<sub>3</sub><sup>2</sup> x<sub>3</sub> 1}}
+
+xo = -bx / 2 * a
+
+yo = -by / 2 * a
+
+
+[circumcircle]:http://mathworld.wolfram.com/Circumcircle.html

lib/math_demo/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 # A wrapper for version
 module MathDemo
-  VERSION = '0.0.1'.freeze
+  VERSION = '0.1.0'.freeze
 end