[GitHub] everwind opened a new issue #7573: how to use autograd in c++

[gi...@git.apache.org]

everwind opened a new issue #7573: how to use autograd in c++
URL: https://github.com/apache/incubator-mxnet/issues/7573
 
 
   ### the example of autograd in python:
   
   x = mx.nd.array([1,2,3,4])
   x.attach_grad()
   with mx.autograd.record():
       y = x * x + 1
    y.backward()
   print(x.grad)
   
   I try to implements C++ version for the above example .  and the code is:
   void test()
   {
       Context device(DeviceType::kCPU, 0);
       NDArray x = NDArray(Shape(3, 4), device, true);
       NDArray grad_x = NDArray(Shape(3, 4), device, true);
       mx_uint array[1] = {1};
       void* p_x[1] = { static_cast<void*>(&x)};
       void* p_grad_x[1] = { static_cast<void*>(&grad_x)};
       MXAutogradMarkVariables(1, p_x, array, p_grad_x);  // the corresponding python code is:  x.attach_grad()
       MXNotifyShutdown();
   }
   but i get a  Segmentation fault (core dumped).   can mxnet provide a c++ version example of the autograd ? 
   #######the gdb information is 
   (gdb) bt
   #0  0x0000000000406126 in __gnu_cxx::__exchange_and_add(int volatile*, int) ()
   #1  0x00000000004061bb in __gnu_cxx::__exchange_and_add_dispatch(int*, int) ()
   #2  0x00000000004280db in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() ()
   #3  0x00007ffff2325dc2 in mxnet::autograd::AutogradRuntime::MarkVariables(std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&, std::vector<unsigned int, std::allocator<unsigned int> > const&, std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&) () from ./libmxnet.so
   #4  0x00007ffff26445fc in MXAutogradMarkVariables () from ./libmxnet.so
   #5  0x000000000040ede8 in test() ()
   #6  0x000000000040ee90 in main ()
   (gdb) f 3
   #3  0x00007ffff2325dc2 in mxnet::autograd::AutogradRuntime::MarkVariables(std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&, std::vector<unsigned int, std::allocator<unsigned int> > const&, std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&) () from ./libmxnet.so
   
   
 
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