sigmoid in ruby

doolin · Jan 26, 2016 · 6e6ec11 · 6e6ec11
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diff --git a/nb/dss/nn/ruby/lib/perceptron.rb b/nb/dss/nn/ruby/lib/perceptron.rb
@@ -13,4 +13,8 @@ def step_function(x)
   def think(u)
     step_function(@weights.dot(u).to_f + @bias)
   end
+
+  def sigmoid(t)
+    1.0 / (1.0 + Math.exp(-t))
+  end
 end
diff --git a/nb/dss/nn/ruby/spec/perceptron_spec.rb b/nb/dss/nn/ruby/spec/perceptron_spec.rb
@@ -70,4 +70,10 @@
       expect(subject.think(u)).to be 0
     end
   end
+
+  describe "sigmoid" do
+    it "computes a sigmoid" do
+      expect(subject.sigmoid(1.0)).to be 1.0
+    end
+  end
 end