From 4c45f2f32ea288e8c60a71a721ce57c594165519 Mon Sep 17 00:00:00 2001
From: kshitij12345 <kshitijkalambarkar@gmail.com>
Date: Thu, 11 Jul 2019 20:00:10 +0530
Subject: [PATCH] add small note for computation

---
 src/operator/tensor/elemwise_unary_op_trig.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/operator/tensor/elemwise_unary_op_trig.cc b/src/operator/tensor/elemwise_unary_op_trig.cc
index 409f99cba799..0199ed2318ce 100644
--- a/src/operator/tensor/elemwise_unary_op_trig.cc
+++ b/src/operator/tensor/elemwise_unary_op_trig.cc
@@ -217,6 +217,7 @@ MXNET_OPERATOR_REGISTER_BINARY_WITH_SPARSE_CPU_DR(_backward_arccos,
       // f(x) = arccos(x)
       // n: f'(x) = -1/(1-x^2)^1/2
       // f''(x) = f'(x) * x/(1-x^2)
+      // Note: x/(1-x^2) = x * f'(x)^2
       auto dydx = n->inputs[0];
       auto x = n->inputs[1];
       auto dydx_mul_grad_x = nnvm::NodeEntry{n};