From db06c97789bb759a8017a793a7dd629481a87cb3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=20van=20Merri=C3=ABnboer?=
 <bart.vanmerrienboer@gmail.com>
Date: Fri, 27 May 2016 16:26:55 -0400
Subject: [PATCH 1/2] Fix zero gradient for subtensor assignment.

The variable that is being assigned has its gradient correctly
calculated (g[k]) but later on when the gradient of the variable being
assigned to is calculated g[k] is set to 0. This gives the correct
gradient for the variable being assigned to, but because it shares the
same storage it actually overrides the earlier gradient incorrectly to
zero. This fixes that.
---
 src/gradfuns.lua | 7 ++++++-
 test/test.lua    | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/gradfuns.lua b/src/gradfuns.lua
index 80fade1..24306e7 100644
--- a/src/gradfuns.lua
+++ b/src/gradfuns.lua
@@ -152,7 +152,12 @@ functions.set = {
       return nil
    end,
    function(g, ans, x, k, v)
-      return g[k]
+      local gk = getValue(g[k])
+      if type(gk) == 'number' then
+        return gk
+      else
+        return torch.clone(gk)
+      end
    end,
 }
 
diff --git a/test/test.lua b/test/test.lua
index 9bdaad3..5adc28f 100644
--- a/test/test.lua
+++ b/test/test.lua
@@ -1687,6 +1687,11 @@ local tests = {
          return torch.sum(xc)
       end
       tester:assert(gradcheck(f4,{x=torch.randn(10,10),y=torch.randn(3)}), "Incorrect gradient")
+      local f5 = function(params)
+         params.x[2] = params.y*2.0
+         return torch.sum(params.x)
+      end
+      tester:assert(gradcheck(f5,{x=torch.randn(10,10),y=torch.randn(10)}), "Incorrect gradient")
    end,
 
    ScalarSigmoid = function()

From 1fa109ab53cbed20e986f6514d72caf1adc30a15 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=20van=20Merri=C3=ABnboer?=
 <bart.vanmerrienboer@gmail.com>
Date: Wed, 13 Jul 2016 13:08:48 -0400
Subject: [PATCH 2/2] Add overwriting test, fix indexing test

---
 src/gradcheck.lua | 13 ++++++++++++-
 test/test.lua     |  5 +++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/gradcheck.lua b/src/gradcheck.lua
index 4e31780..7dc8cf5 100644
--- a/src/gradcheck.lua
+++ b/src/gradcheck.lua
@@ -1,5 +1,6 @@
 -- Autograd
 local autograd = require 'autograd'
+local util = require 'autograd.util'
 
 -- Perturbation (finite diffs):
 local perturbation = 1e-6
@@ -12,20 +13,30 @@ local function jacobianFromAutograd(func, inputs, key)
    -- Autograd:
    local df = autograd(func)
    local grads = df(table.unpack(inputs))
-   local gradsVerify = df(table.unpack(inputs))
 
    -- Find grad:
    local g = autograd.util.nestedGet(grads, key)
+   local g_clone
+   if torch.isTensor(g) then
+     g_clone = g:clone()
+   end
+
+   -- Get the grad again
+   local gradsVerify = df(table.unpack(inputs))
    local gVerify = autograd.util.nestedGet(gradsVerify, key)
    local err
+   local overwrite_err = 0
    if torch.isTensor(g) then
       err = (g - gVerify):abs():max()
+      overwrite_err = (g - g_clone):abs():max()
    else
       err = torch.abs(g - gVerify)
    end
 
    if err ~= 0 then
       error("autograd gradient not deterministic")
+   elseif overwrite_err ~= 0 then
+      error("autograd gradient overwritten when called twice")
    end
 
    -- Return grads:
diff --git a/test/test.lua b/test/test.lua
index 5adc28f..8c8e8eb 100644
--- a/test/test.lua
+++ b/test/test.lua
@@ -1688,8 +1688,9 @@ local tests = {
       end
       tester:assert(gradcheck(f4,{x=torch.randn(10,10),y=torch.randn(3)}), "Incorrect gradient")
       local f5 = function(params)
-         params.x[2] = params.y*2.0
-         return torch.sum(params.x)
+         local xc = torch.clone(params.x)
+         xc[2] = params.y * 2.0
+         return torch.sum(xc)
       end
       tester:assert(gradcheck(f5,{x=torch.randn(10,10),y=torch.randn(10)}), "Incorrect gradient")
    end,