From f8101400c2a4964302d59bc75961db54d70ada55 Mon Sep 17 00:00:00 2001
From: aodhneine <aodhneine@protonmail.ch>
Date: Sun, 15 Nov 2020 21:59:25 +0000
Subject: [PATCH] Add tanh method to tensor

---
 pygrad/tensor.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/pygrad/tensor.py b/pygrad/tensor.py
index 0c0e9e9..0f0cc8b 100644
--- a/pygrad/tensor.py
+++ b/pygrad/tensor.py
@@ -92,6 +92,18 @@ class Tensor:
     tensor._back = back
     return tensor
 
+  def tanh(self):
+    tensor = Tensor(np.tanh(self.value))
+    tensor._save(self)
+
+    def back(upstream):
+      # dtanh(x)/dx = 1 - tanh2(x)
+      a, = tensor._parents
+      return [1 - np.dot(np.tanh(a.value) ** 2, upstream)]
+
+    tensor._back = back
+    return tensor
+
   # TODO Compute gradients only for tensors that need it.
   def _backprop(self, upstream):
     # Backprop through the tensor iff it has any parents.