gaussian error function

clab · Dec 8, 2015 · e1f5f3c · e1f5f3c
1 parent d2ef1d9
commit e1f5f3c
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diff --git a/cnn/expr.cc b/cnn/expr.cc
@@ -36,6 +36,7 @@ Expression colwise_add(const Expression& x, const Expression& bias) { return Exp
 Expression contract3d_1d(const Expression& x, const Expression& y) { return Expression(x.pg, x.pg->add_function<InnerProduct3D_1D>({x.i, y.i})); }
 Expression contract3d_1d(const Expression& x, const Expression& y, const Expression& b) { return Expression(x.pg, x.pg->add_function<InnerProduct3D_1D>({x.i, y.i, b.i})); }
 
+Expression erf(const Expression& x) { return Expression(x.pg, x.pg->add_function<Erf>({x.i})); }
 Expression tanh(const Expression& x) { return Expression(x.pg, x.pg->add_function<Tanh>({x.i})); }
 Expression log(const Expression& x) { return Expression(x.pg, x.pg->add_function<Log>({x.i})); }
 Expression exp(const Expression& x) { return Expression(x.pg, x.pg->add_function<Exp>({x.i})); }

diff --git a/cnn/expr.h b/cnn/expr.h
@@ -50,6 +50,7 @@ Expression contract3d_1d(const Expression& x, const Expression& y);
 // z_ij = x_ijk * y_k + b_ij
 Expression contract3d_1d(const Expression& x, const Expression& y, const Expression& b);
 
+Expression erf(const Expression& x);
 Expression tanh(const Expression& x);
 Expression exp(const Expression& x);
 Expression square(const Expression& x);

diff --git a/cnn/functors.h b/cnn/functors.h
@@ -84,6 +84,12 @@ struct FNegate {
   }
 };
 
+struct FErf {
+  CNN_DEVICE_FUNC inline float operator()(float x) const {
+    return erff(x);
+  }
+};
+
 struct FTanh {
   CNN_DEVICE_FUNC inline float operator()(float x) const {
 #ifdef FAST_TANH
@@ -103,6 +109,12 @@ struct FMaxBackwardInv {
   }
 };
 
+struct FErfBackward {
+  CNN_DEVICE_FUNC inline float operator()(float x, float d) const {
+    return 1.1283791670955125738961589f * expf(-x * x) * d;
+  }
+};
+
 struct FTanhBackward {
   CNN_DEVICE_FUNC inline float operator()(float t, float d) const {
     return (1.f - t * t) * d;

diff --git a/cnn/nodes-common.cc b/cnn/nodes-common.cc
@@ -300,6 +300,17 @@ Dim Average::dim_forward(const vector<Dim>& xs) const {
   return d;
 }
 
+string Erf::as_string(const vector<string>& arg_names) const {
+  ostringstream s;
+  s << "erf(" << arg_names[0] << ')';
+  return s.str();
+}
+
+Dim Erf::dim_forward(const vector<Dim>& xs) const {
+  assert(xs.size() == 1);
+  return xs[0];
+}
+
 string Tanh::as_string(const vector<string>& arg_names) const {
   ostringstream s;
   s << "tanh(" << arg_names[0] << ')';

diff --git a/cnn/nodes.cc b/cnn/nodes.cc
@@ -506,6 +506,20 @@ void Average::backward_impl(const vector<const Tensor*>& xs,
   *dEdxi += (*dEdf / xs.size());
 }
 
+void Erf::forward_impl(const vector<const Tensor*>& xs, Tensor& fx) const {
+  auto x = **xs[0];
+  (*fx) = x.unaryExpr(FErf());
+}
+
+void Erf::backward_impl(const vector<const Tensor*>& xs,
+                        const Tensor& fx,
+                        const Tensor& dEdf,
+                        unsigned i,
+                        Tensor& dEdxi) const {
+  auto x = **xs[0];
+  *dEdxi += x.binaryExpr(*dEdf, FErfBackward());
+}
+
 void Tanh::forward_impl(const vector<const Tensor*>& xs, Tensor& fx) const {
 #if HAVE_CUDA
   gpu::vtanh(fx.d.size(), xs[0]->v, fx.v);

diff --git a/cnn/nodes.h b/cnn/nodes.h
@@ -226,6 +226,19 @@ struct ConstantMinusX : public Node {
   real c;
 };
 
+// y = erf x_1
+struct Erf : public Node {
+  explicit Erf(const std::initializer_list<VariableIndex>& a) : Node(a) {}
+  std::string as_string(const std::vector<std::string>& arg_names) const override;
+  Dim dim_forward(const std::vector<Dim>& xs) const override;
+  void forward_impl(const std::vector<const Tensor*>& xs, Tensor& fx) const override;
+  void backward_impl(const std::vector<const Tensor*>& xs,
+                  const Tensor& fx,
+                  const Tensor& dEdf,
+                  unsigned i,
+                  Tensor& dEdxi) const override;
+};
+
 // y = tanh x_1
 struct Tanh : public Node {
   explicit Tanh(const std::initializer_list<VariableIndex>& a) : Node(a) {}