larroy commented on issue #14991: Second order gradient wrt inputs, expected behaviour. URL: https://github.com/apache/incubator-mxnet/issues/14991#issuecomment-494174917 Which branch are you using? I'm getting the following when running your example: ``` File "/home/ANT.AMAZON.COM/pllarroy/devel/mxnet/python/mxnet/ndarray/ndarray.py", line 2216, in backward ctypes.c_void_p(0))) File "/home/ANT.AMAZON.COM/pllarroy/devel/mxnet/python/mxnet/base.py", line 254, in check_call raise MXNetError(py_str(_LIB.MXGetLastError())) mxnet.base.MXNetError: [15:37:55] /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/src/imperative/imperative.cc:357: Check failed: var_nodes.variable_nodes.size() > 0 (0 vs. 0) : There are no inputs in computation graph that require gradients. Stack trace: [bt] (0) /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/cmake-build-debug/libmxnet.so(dmlc::LogMessageFatal::~LogMessageFatal()+0x4a) [0x7f6590fc7b5e] [bt] (1) /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/cmake-build-debug/libmxnet.so(mxnet::Imperative::CreateGradientVariableNodes(std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&, std::vector<nnvm::NodeEntry, std::allocator<nnvm::NodeEntry> > const&)+0x535) [0x7f65911c63e1] [bt] (2) /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/cmake-build-debug/libmxnet.so(mxnet::Imperative::Backward(std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&, std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&, std::vector<mxnet::NDArray*, std::allocator<mxnet::NDArray*> > const&, bool, bool, bool)+0x2ff) [0x7f65911c6ae1] [bt] (3) /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/cmake-build-debug/libmxnet.so(MXAutogradBackwardEx+0x249) [0x7f6591034c12] [bt] (4) /usr/lib/x86_64-linux-gnu/libffi.so.6(ffi_call_unix64+0x4c) [0x7f65aac85dae] [bt] (5) /usr/lib/x86_64-linux-gnu/libffi.so.6(ffi_call+0x22f) [0x7f65aac8571f] [bt] (6) /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/py3_venv/lib/python3.6/lib-dynload/_ctypes.cpython-36m-x86_64-linux-gnu.so(_ctypes_callproc+0x2b4) [0x7f65aae99524] [bt] (7) /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/py3_venv/lib/python3.6/lib-dynload/_ctypes.cpython-36m-x86_64-linux-gnu.so(+0x11b93) [0x7f65aae99b93] [bt] (8) /home/ANT.AMAZON.COM/pllarroy/devel/mxnet/py3_venv/bin/python(_PyObject_FastCallKeywords+0x19c) [0x5a730c] -------------------- >> begin captured logging << -------------------- common: INFO: Setting module np/mx/python random seeds, use MXNET_MODULE_SEED=1526948194 to reproduce. --------------------- >> end captured logging << --------------------- ```
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