diff --git a/examples/tsp.rb b/examples/tsp.rb
index 1a22729..a94630c 100644
--- a/examples/tsp.rb
+++ b/examples/tsp.rb
@@ -10,23 +10,40 @@
 require 'alns/select/roulette_wheel'
 require 'alns/stop/max_iterations'
 require 'alns/stop/max_runtime'
+require 'alns/random/random'
 
 module TSP
   def self.solve
     write_dot = false
+    seed = 1234
+    secure_random = false
 
     OptionParser.new do |parser|
       parser.banner = 'Usage: tsp.rb [options]'
 
-      parser.on('-d', '--dot', 'write a dot file with result') do |v|
+      parser.on('-d', '--dot', 'write a dot file with the result') do
         write_dot = true
       end
+
+      parser.on('-sSEED', '--seed=SEED', Integer, 'specify seed') do |v|
+        seed = v
+      end
+
+      parser.on('-r', '--secure-random', 'use secure random') do
+        secure_random = true
+      end
     end.parse!
 
     nodes = make_nodes(COORDS)
     dists = make_dists(COORDS)
 
-    solver = ALNS::Solver.new(Random.new(1234))
+    rnd = if secure_random
+            ALNS::Random::Random.new
+          else
+            Random.new(seed)
+          end
+
+    solver = ALNS::Solver.new(rnd)
 
     init_sol = TspState.new(nodes, {}, dists)
     init_sol = greedy_repair(init_sol, solver.rnd)
@@ -256,17 +273,21 @@ def initialize(nodes, edges, dists)
 
     def initialize_copy(original)
       super
-      @nodes = original.nodes
+      # @nodes is frozen
       @edges = original.edges.dup
-      @dists = original.dists
+      # @dists is frozen
+      @objective = nil
     end
 
     def objective
-      total_dist = 0.0
-      @edges.each do |from, to|
-        total_dist += @dists[from][to]
+      if @objective.nil?
+        total_dist = 0.0
+        @edges.each do |from, to|
+          total_dist += @dists[from][to]
+        end
+        @objective = total_dist
       end
-      total_dist
+      @objective
     end
   end
 
diff --git a/lib/alns/math.rb b/lib/alns/math.rb
index f6d5492..e8d07eb 100644
--- a/lib/alns/math.rb
+++ b/lib/alns/math.rb
@@ -1,12 +1,6 @@
 # frozen_string_literal: true
 
 module ALNS
-  EPSILON = 1e-9
-
-  def self.close?(a, b, epsilon = EPSILON) # rubocop:disable Naming/MethodParameterName
-    (a - b).abs <= epsilon
-  end
-
   def self.weighted_random_index(rnd, weights)
     raise 'Invalid weights: Array is empty' if weights.empty?
     return 0 if weights.size == 1
@@ -17,9 +11,10 @@ def self.weighted_random_index(rnd, weights)
     weights.each_with_index do |weight, index|
       adjusted_value -= weight
 
-      return index if adjusted_value <= 0 || close?(adjusted_value, 0)
+      return index if adjusted_value <= 0
     end
 
-    raise "Arithmetic error: sum=#{total_sum}, adjusted_value=#{adjusted_value}, weights=#{weights.inspect}"
+    # we will only be here when errors accumulate
+    weights.length - 1
   end
 end
diff --git a/lib/alns/random/random.rb b/lib/alns/random/random.rb
new file mode 100644
index 0000000..cb95301
--- /dev/null
+++ b/lib/alns/random/random.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require 'securerandom'
+
+module ALNS
+  module Random
+    class Random
+      def rand(max = nil)
+        if max.nil?
+          SecureRandom.random_number
+        else
+          SecureRandom.random_number(max)
+        end
+      end
+    end
+  end
+end
diff --git a/test/math_test.rb b/test/math_test.rb
index 84a87dc..8eecb16 100644
--- a/test/math_test.rb
+++ b/test/math_test.rb
@@ -9,11 +9,6 @@ def setup
     @rnd = Random.new(123)
   end
 
-  def test_close
-    assert ALNS.close?(1, 1.0000000001)
-    assert !ALNS.close?(1, 1.0000001)
-  end
-
   def test_weighted_random_index
     tests = [
       { weights: [1.0], want: 0 }, # one element