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@@ -5,19 +5,27 @@ class Array
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     if size == y.size
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       return GSL::Stats.correlation1(self, y)
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     else
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-      raise ArgumentError, "cannot correlated two differently-sized arrays"
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+      raise ArgumentError, "cannot correlate two differently-sized arrays"
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     end
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   end
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+  # Returns the arithmetic mean of the elements of the array.
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   def mean
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     return GSL::Stats.mean1(self)
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   end
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+  # Returns the variance of the elements of the array.
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   def variance
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     return GSL::Stats.variance1(self)
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   end
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+  # Returns the standard distribution of the elements of the array.
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   def sd
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-    return GSL::Stats::sd1(self)
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+    return GSL::Stats.sd1(self)
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+  end
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+  
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+  # Returns the Tanimoto coefficient of the array and +y+.
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+  def tanimoto_coefficient(y)
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+    return GSL::Similarity.tanimoto_coefficient(self, y)
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   end
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 end
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@@ -30,4 +30,11 @@ describe Array do
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       [2, 2, 2].sd.should be_close(0.0, 0.0001)
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     end
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   end
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+  
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+  describe "calculating the Tanimoto coefficient" do
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+    it "should return a real number" do
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+      [1, 2, 3].tanimoto_coefficient([1, 2, 3]).should be_close(1.0, 0.0001)
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+      [1, 2, 3].tanimoto_coefficient([4, 5, 6]).should be_close(0.0, 0.0001)
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+    end
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+  end
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 end
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