From 1613c4a241639792b711b3c0c8dd3ae9d8f03a19 Mon Sep 17 00:00:00 2001
From: Pavan Yalamanchili <contact@pavanky.com>
Date: Sun, 23 Jul 2017 23:01:26 -0700
Subject: [PATCH] Adding abs function to autograd

---
 include/af/autograd/Functions.hpp |  2 +-
 src/autograd/Functions.cpp        | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/af/autograd/Functions.hpp b/include/af/autograd/Functions.hpp
index 182aba0..119d9c0 100644
--- a/include/af/autograd/Functions.hpp
+++ b/include/af/autograd/Functions.hpp
@@ -73,6 +73,6 @@ namespace af {
         Variable matmulTN(const Variable &lhs, const Variable &rhs);
         Variable matmulNT(const Variable &lhs, const Variable &rhs);
 
-
+        Variable abs(const Variable &val);
     }
 }
diff --git a/src/autograd/Functions.cpp b/src/autograd/Functions.cpp
index d754689..09c14ef 100644
--- a/src/autograd/Functions.cpp
+++ b/src/autograd/Functions.cpp
@@ -375,5 +375,17 @@ namespace af {
             };
             return Variable(result, {lhs, rhs}, grad_func);
         }
+
+        Variable abs(const Variable &val)
+        {
+            auto result = af::abs(val.array());
+            auto grad_func = [](std::vector<Variable> &inputs, const Variable &grad_output) {
+                // af::sign returns signbit
+                // Convert it into -1, 1
+                auto sign = Variable(1 - 2 * af::sign(inputs[0].array()), false);
+                inputs[0].addGrad(sign * grad_output);
+            };
+            return Variable(result, {val}, grad_func);
+        }
     }
 }