From f3ac4d8e3530d4c42cfbcf979cf3cf9ad515a080 Mon Sep 17 00:00:00 2001
From: Abhinav Arora <abhinavarora28@gmail.com>
Date: Fri, 27 Oct 2017 16:50:26 -0700
Subject: [PATCH] Adding L1 Decay Regularizer (#5173)

---
 python/paddle/v2/framework/regularizer.py     | 44 ++++++++++++++++++-
 .../v2/framework/tests/test_regularizer.py    | 34 ++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/python/paddle/v2/framework/regularizer.py b/python/paddle/v2/framework/regularizer.py
index cc7ebbe97e5..5111ac5566f 100644
--- a/python/paddle/v2/framework/regularizer.py
+++ b/python/paddle/v2/framework/regularizer.py
@@ -1,6 +1,8 @@
 import paddle.v2.framework.framework as framework
 
-__all__ = ['append_regularization_ops', 'L2DecayRegularizer']
+__all__ = [
+    'append_regularization_ops', 'L2DecayRegularizer', 'L1DecayRegularizer'
+]
 
 
 def append_regularization_ops(parameters_and_grads):
@@ -97,3 +99,43 @@ class L2DecayRegularizer(WeightDecayRegularizer):
             attrs={"scale": self._regularization_coeff})
 
         return decay
+
+
+class L1DecayRegularizer(WeightDecayRegularizer):
+    """Implements the L1 Weight Decay Regularization
+    """
+
+    def __init__(self, regularization_coeff=0.0):
+        assert regularization_coeff is not None
+        super(L1DecayRegularizer, self).__init__()
+        self._regularization_coeff = regularization_coeff
+
+    def __call__(self, param, block):
+        """Add L1 weight decay ops to network
+
+        Adds L1 weight decay ops.
+        L1WeightDecay = reg_coeff * sign(parameter)
+
+        Args:
+            param: parameter variable for which regularization is applied
+            block: block in which variable is to be created
+
+        Returns:
+            new variable for weight decay
+        """
+        assert isinstance(param, framework.Parameter)
+        assert isinstance(block, framework.Block)
+        decay = block.create_var(
+            dtype="float32", shape=param.shape, lod_level=param.lod_level)
+        # Append sign op
+        block.append_op(
+            type='sign', inputs={"X": param}, outputs={"Out": decay})
+
+        # Append scale op to the output of sign op
+        block.append_op(
+            type='scale',
+            inputs={"X": decay},
+            outputs={"Out": decay},
+            attrs={"scale": self._regularization_coeff})
+
+        return decay
diff --git a/python/paddle/v2/framework/tests/test_regularizer.py b/python/paddle/v2/framework/tests/test_regularizer.py
index 06a892ada19..b21dceb584b 100644
--- a/python/paddle/v2/framework/tests/test_regularizer.py
+++ b/python/paddle/v2/framework/tests/test_regularizer.py
@@ -39,5 +39,39 @@ class TestL2DecayRegularizer(unittest.TestCase):
         self.assertEqual(block.ops[-2].type, 'scale')
 
 
+class TestL1DecayRegularizer(unittest.TestCase):
+    def test_l2decay_regularizer(self):
+        program = framework.Program()
+        block = program.global_block()
+        mul_x = block.create_parameter(
+            dtype="float32",
+            shape=[5, 10],
+            lod_level=0,
+            name="mul.x",
+            regularizer=regularizer.L1DecayRegularizer(0.5))
+        self.assertTrue(mul_x.regularizer is not None)
+        self.assertTrue(
+            isinstance(mul_x.regularizer, regularizer.L1DecayRegularizer))
+        mul_y = block.create_var(
+            dtype="float32", shape=[10, 8], lod_level=0, name="mul.y")
+        mul_out = block.create_var(
+            dtype="float32", shape=[5, 8], lod_level=0, name="mul.out")
+        block.append_op(
+            type="mul",
+            inputs={"X": mul_x,
+                    "Y": mul_y},
+            outputs={"Out": mul_out},
+            attrs={"x_num_col_dims": 1})
+        params_grads = append_backward_ops(mul_out)
+        self.assertEqual(len(params_grads), 1)
+        count_ops = len(block.ops)
+        params_grads = optimizer.append_regularization_ops(params_grads)
+        self.assertEqual(len(params_grads), 1)
+        self.assertEqual(len(block.ops), count_ops + 3)
+        self.assertEqual(block.ops[-1].type, 'elementwise_add')
+        self.assertEqual(block.ops[-2].type, 'scale')
+        self.assertEqual(block.ops[-3].type, 'sign')
+
+
 if __name__ == '__main__':
     unittest.main()
-- 
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