added softsign to sandbox

theano/sandbox/softsign.py

+
+import theano
+import numpy
+import theano.tensor
+
+class ScalarSoftsign(theano.scalar.UnaryScalarOp):
+    @staticmethod
+    def static_impl(x):
+        return x / (1.0 + abs(x))
+    def impl(self, x):
+        return ScalarSoftsign.static_impl(x)
+    def grad(self, (x, ), (gz, )):
+        if 'float' in x.type.dtype:
+            d = (1.0 + abs(x))
+            return [gz / (d * d)]
+        else:
+            return NotImplemented
+    def c_code(self, node, name, (x, ), (z, ), sub):
+        if node.inputs[0].type in [theano.scalar.float32, theano.scalar.float64]:
+            return "%(z)s = %(x)s / (1.0+fabs(%(x)s));" % locals()
+        raise NotImplementedError('only floating point x is implemented')
+scalar_softsign = ScalarSoftsign(theano.scalar.upgrade_to_float, name='scalar_softsign')
+softsign = theano.tensor.Elemwise(scalar_softsign, name='softsign')
+