Initial data commit

Task/Statistics-Normal-distribution/Ruby/statistics-normal-distribution-1.rb

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+# Class to implement a Normal distribution, generated from a Uniform distribution.
+# Uses the Marsaglia polar method.
+
+class NormalFromUniform
+  # Initialize an instance.
+  def initialize()
+    @next = nil
+  end
+  # Generate and return the next Normal distribution value.
+  def rand()
+    if @next
+      retval, @next = @next, nil
+      return retval
+    else
+      u = v = s = nil
+      loop do
+        u = Random.rand(-1.0..1.0)
+        v = Random.rand(-1.0..1.0)
+        s = u**2 + v**2
+        break if (s > 0.0) && (s <= 1.0)
+      end
+      f = Math.sqrt(-2.0 * Math.log(s) / s)
+      @next = v * f
+      return u * f
+    end
+  end
+end

Task/Statistics-Normal-distribution/Ruby/statistics-normal-distribution-2.rb

@@ -0,0 +1,30 @@
+require('enumerable/statistics')
+
+def show_stats_and_histogram(data, bins)
+  puts("size = #{data.length}  mean = #{data.mean()}  stddev = #{data.stdev()}")
+  hist = data.histogram(bins)
+  scale = 100.0 / hist.weights.max
+  inx_beg = nil
+  inx_end = nil
+  hist.weights.length.times do |inx|
+    histstars = (0.5 + (scale * hist.weights[inx])).to_i
+    inx_beg = inx if !inx_beg && (histstars > 0)
+    inx_end = inx if (histstars > 0)
+  end
+  (inx_beg..inx_end).each do |inx|
+    bincenter = 0.5 * (hist.edges[inx] + hist.edges[inx + 1])
+    histstars = (0.5 + (scale * hist.weights[inx])).to_i
+    puts('%6.2f: %s' % [bincenter, '*' * histstars])
+  end
+end
+
+puts
+puts('Uniform random number generator:')
+show_stats_and_histogram(1000000.times.map { Random.rand(-1.0..1.0) }, 20)
+
+puts
+puts('Normal random numbers using the Marsaglia polar method:')
+gen_normal = NormalFromUniform.new
+show_stats_and_histogram(100.times.map { gen_normal.rand }, 40)
+show_stats_and_histogram(10000.times.map { gen_normal.rand }, 60)
+show_stats_and_histogram(1000000.times.map { gen_normal.rand }, 120)