add softsign activation.

paddle/gserver/activations/ActivationFunction.cpp

@@ -212,6 +212,37 @@ Error __must_check backward(Argument& act) {
 }
 END_DEFINE_ACTIVATION(sequence_softmax)
 
+/*
+ * @brief SoftSign Activation.
+ * \f[
+ * f(z) = \frac{z}{1 + |z|}
+ * \f]
+ */
+BEGIN_DEFINE_ACTIVATION(softsign)
+private:
+MatrixPtr denominator_;
+
+Error __must_check forward(Argument& act) {
+  size_t height = act.value->getHeight();
+  size_t width = act.value->getWidth();
+  Matrix::resizeOrCreate(
+      denominator_, height, width, false, useGpu(act.deviceId));
+  denominator_->assign(*act.value);
+  denominator_->abs2();
+  denominator_->add(1.);
+
+  act.value->dotDiv(*act.value, *denominator_);
+  return Error();
+}
+
+Error __must_check backward(Argument& act) {
+  denominator_->square2();
+  denominator_->scalarDiv(*denominator_, 1.);
+  act.grad->dotMul(*act.grad, *denominator_);
+  return Error();
+}
+END_DEFINE_ACTIVATION(softsign)
+
 /**
  * @brief Relu Activation.
  * forward. y = max(0, z)

python/paddle/trainer_config_helpers/activations.py

@@ -17,7 +17,8 @@
     "IdentityActivation", "LinearActivation", 'SequenceSoftmaxActivation',
     'ExpActivation', "ReluActivation", "BReluActivation", "SoftReluActivation",
     "STanhActivation", "AbsActivation", "SquareActivation", "BaseActivation",
-    "LogActivation", "SqrtActivation", "ReciprocalActivation"
+    "LogActivation", "SqrtActivation", "ReciprocalActivation",
+    "SoftSignActivation"
 ]
 
 
@@ -243,8 +244,20 @@ class ReciprocalActivation(BaseActivation):
     Reciprocal Activation.
 
     .. math::
-       f(z) = 1/z
+       f(z)=\\frac{1}{z}
     """
 
     def __init__(self):
         BaseActivation.__init__(self, 'reciprocal', False)
+
+
+class SoftSignActivation(BaseActivation):
+    """
+    SoftSign Activation.
+
+    .. math::
+       f(z)=\\frac{z}{1 + |z|}
+    """
+
+    def __init__(self):
+        BaseActivation.__init__(self, 'softsign', False)

python/paddle/v2/fluid/tests/test_sequence_slice_op.py

@@ -3,6 +3,7 @@
 import sys
 from op_test import OpTest
 
+
 class TestSequenceSliceOp(OpTest):
     def set_data(self):
         self.init_test_case()
@@ -13,12 +14,12 @@ def set_data(self):
         length = np.array(self.length).astype("int64")
 
         self.inputs = {'X': (x, lod), 'Offset': offset, 'Length': length}
-        outs = [] #np.zeros((100, 3, 2)).astype('float32')
+        outs = []  #np.zeros((100, 3, 2)).astype('float32')
         out_lod = [[0]]
         out_lod_offset = 0
         for i in range(len(offset)):
-            sub_x = x[lod[0][i] + offset[i, 0]: lod[0]
-                      [i] + offset[i, 0] + length[i, 0], :]
+            sub_x = x[lod[0][i] + offset[i, 0]:lod[0][i] + offset[i, 0] +
+                      length[i, 0], :]
             out_lod_offset = out_lod_offset + len(sub_x)
             outs.append(sub_x)
             out_lod[0].append(out_lod_offset)
@@ -41,5 +42,6 @@ def test_check_output(self):
     def test_check_grad(self):
         self.check_grad(['X'], 'Out')
 
+
 if __name__ == '__main__':
     unittest.main()