src/c_api/c_api_ndarray.cc - mxnet - Git at Google

 /*
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
  * distributed with this work for additional information
  * regarding copyright ownership.  The ASF licenses this file
  * to you under the Apache License, Version 2.0 (the
  * "License"); you may not use this file except in compliance
  * with the License.  You may obtain a copy of the License at
  *
  *   http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing,
  * software distributed under the License is distributed on an
  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  * KIND, either express or implied.  See the License for the
  * specific language governing permissions and limitations
  * under the License.
  */

 /*!
  *  Copyright (c) 2016 by Contributors
  * \file c_api_ndarray.cc
  * \brief C API of mxnet
  */

 #include <mxnet/base.h>
 #include <mxnet/c_api.h>
 #include <mxnet/operator.h>
 #include <mxnet/operator_util.h>
 #include <mxnet/op_attr_types.h>
 #include <mxnet/imperative.h>
 #include <nnvm/node.h>
 #include <nnvm/op_attr_types.h>
 #include <string>
 #include "./c_api_common.h"
 #include "../common/utils.h"
 #include "../common/exec_utils.h"
 #include "../imperative/imperative_utils.h"
 #include "../imperative/cached_op.h"

 using namespace mxnet;

 void SetNDInputsOutputs(const nnvm::Op* op,
                         std::vector<NDArray*>* ndinputs,
                         std::vector<NDArray*>* ndoutputs,
                         int num_inputs,
                         const NDArrayHandle *inputs,
                         int *num_outputs,
                         int infered_num_outputs,
                         int num_visible_outputs,
                         NDArrayHandle **outputs) {
   NDArray** out_array = *reinterpret_cast<NDArray***>(outputs);

   ndinputs->clear();
   ndinputs->reserve(num_inputs);
   for (int i = 0; i < num_inputs; ++i) {
     ndinputs->emplace_back(reinterpret_cast<NDArray*>(inputs[i]));
   }

   ndoutputs->clear();
   ndoutputs->reserve(infered_num_outputs);
   if (out_array == nullptr) {
     for (int i = 0; i < infered_num_outputs; ++i) {
       ndoutputs->emplace_back(new NDArray());
     }
     *num_outputs = num_visible_outputs;
   } else {
     CHECK(*num_outputs == infered_num_outputs || *num_outputs == num_visible_outputs)
       << "Operator expects " << infered_num_outputs << " (all) or "
       << num_visible_outputs << " (visible only) outputs, but got "
       << *num_outputs << " instead.";
     for (int i = 0; i < *num_outputs; ++i) {
       ndoutputs->emplace_back(out_array[i]);
     }
     for (int i = *num_outputs; i < infered_num_outputs; ++i) {
       ndoutputs->emplace_back(new NDArray());
     }
   }
 }

 void MXImperativeInvokeImpl(AtomicSymbolCreator creator,
                             int num_inputs,
                             NDArrayHandle *inputs,
                             int *num_outputs,
                             NDArrayHandle **outputs,
                             int num_params,
                             const char **param_keys,
                             const char **param_vals) {
   const nnvm::Op* op = static_cast<nnvm::Op*>(creator);
   MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();

   nnvm::NodeAttrs attrs = imperative::ParseAttrs(op, num_inputs, num_params,
                                                  param_keys, param_vals);

   int infered_num_outputs;
   int num_visible_outputs;
   imperative::SetNumOutputs(op, attrs, num_inputs, &infered_num_outputs, &num_visible_outputs);

   std::vector<NDArray*> ndinputs, ndoutputs;
   SetNDInputsOutputs(op, &ndinputs, &ndoutputs, num_inputs, inputs,
       num_outputs, infered_num_outputs, num_visible_outputs, outputs);

   auto state = Imperative::Get()->Invoke(Context::CPU(), attrs, ndinputs, ndoutputs);
   if (Imperative::Get()->is_recording()) {
     Imperative::Get()->RecordOp(std::move(attrs), ndinputs, ndoutputs, state);
   }

   for (int i = *num_outputs; i < infered_num_outputs; ++i) delete ndoutputs[i];

   if (*outputs == nullptr) {
     ret->ret_handles.clear();
     ret->ret_handles.reserve(*num_outputs);
     for (int i = 0; i < *num_outputs; ++i) ret->ret_handles.push_back(ndoutputs[i]);
     *outputs = reinterpret_cast<NDArrayHandle*>(dmlc::BeginPtr(ret->ret_handles));
   }
 }

 int MXImperativeInvoke(AtomicSymbolCreator creator,
                        int num_inputs,
                        NDArrayHandle *inputs,
                        int *num_outputs,
                        NDArrayHandle **outputs,
                        int num_params,
                        const char **param_keys,
                        const char **param_vals) {
   API_BEGIN();
   MXImperativeInvokeImpl(creator, num_inputs, inputs, num_outputs, outputs,
                          num_params, param_keys, param_vals);
   API_END();
 }

 int MXImperativeInvokeEx(AtomicSymbolCreator creator,
                          int num_inputs,
                          NDArrayHandle *inputs,
                          int *num_outputs,
                          NDArrayHandle **outputs,
                          int num_params,
                          const char **param_keys,
                          const char **param_vals,
                          const int **out_stypes) {  // outputs storage types
   MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();
   API_BEGIN();
   MXImperativeInvokeImpl(creator, num_inputs, inputs, num_outputs, outputs,
                          num_params, param_keys, param_vals);
   NDArray** out_array = *reinterpret_cast<NDArray***>(outputs);
   ret->out_types.clear();
   ret->out_types.reserve(*num_outputs);
   for (int i = 0; i < *num_outputs; ++i) {
     ret->out_types.emplace_back(out_array[i]->storage_type());
   }
   *out_stypes = dmlc::BeginPtr(ret->out_types);
   API_END();
 }

 int MXCreateCachedOp(SymbolHandle handle,
                      CachedOpHandle *out) {
   nnvm::Symbol* sym = static_cast<nnvm::Symbol*>(handle);

   API_BEGIN();
   auto inputs = sym->ListInputs(nnvm::Symbol::kAll);
   std::vector<std::string> input_names;
   input_names.reserve(inputs.size());
   for (const auto& i : inputs) input_names.push_back(i->attrs.name);
   *out = new CachedOpPtr(new CachedOp(
       *sym, std::vector<std::pair<std::string, std::string> >()));
   API_END();
 }

 int MXCreateCachedOpEx(SymbolHandle handle,
                        int num_flags,
                        const char** keys,
                        const char** vals,
                        CachedOpHandle *out) {
   nnvm::Symbol* sym = static_cast<nnvm::Symbol*>(handle);

   API_BEGIN();
   std::vector<std::pair<std::string, std::string> > flags;
   for (int i = 0; i < num_flags; ++i) {
     flags.push_back({keys[i], vals[i]});
   }
   *out = new CachedOpPtr(new CachedOp(*sym, flags));
   API_END();
 }

 int MXFreeCachedOp(CachedOpHandle handle) {
   CachedOpPtr* g = static_cast<CachedOpPtr*>(handle);
   API_BEGIN();
   delete g;
   API_END();
 }

 int MXInvokeCachedOp(CachedOpHandle handle,
                      int num_inputs,
                      NDArrayHandle *inputs,
                      int *num_outputs,
                      NDArrayHandle **outputs) {
   MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();

   API_BEGIN();
   CachedOpPtr op = *static_cast<CachedOpPtr*>(handle);
   std::vector<NDArray*> ndinputs;
   ndinputs.reserve(num_inputs);
   for (int i = 0; i < num_inputs; ++i) {
     ndinputs.push_back(reinterpret_cast<NDArray*>(inputs[i]));
   }

   std::vector<NDArray*> ndoutputs;
   ndoutputs.reserve(op->num_outputs());
   if (*outputs == nullptr) {
     *num_outputs = op->num_outputs();
     for (int i = 0; i < *num_outputs; ++i) ndoutputs.push_back(new NDArray());
   } else {
     CHECK_EQ(*num_outputs, op->num_outputs())
         << "CachedOp expects " << op->num_outputs() << " outputs, but "
         << *num_outputs << " was given.";
     for (int i = 0; i < *num_outputs; ++i) {
       ndoutputs.push_back(reinterpret_cast<NDArray*>((*outputs)[i]));
     }
   }

   op->Forward(op, ndinputs, ndoutputs);

   if (*outputs == nullptr) {
     ret->ret_handles.clear();
     ret->ret_handles.reserve(*num_outputs);
     for (int i = 0; i < *num_outputs; ++i) {
       ret->ret_handles.push_back(ndoutputs[i]);
     }
     *outputs = dmlc::BeginPtr(ret->ret_handles);
   }

   API_END();
 }

 int MXInvokeCachedOpEx(CachedOpHandle handle,
                        int num_inputs,
                        NDArrayHandle *inputs,
                        int *num_outputs,
                        NDArrayHandle **outputs,
                        const int **out_stypes) {  // outputs storage types
   MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();
   int err = MXInvokeCachedOp(handle, num_inputs, inputs, num_outputs, outputs);
   if (err != 0) return err;
   API_BEGIN();
   NDArray** out_array = reinterpret_cast<NDArray**>(*outputs);
   ret->out_types.clear();
   ret->out_types.reserve(*num_outputs);
   for (int i = 0; i < *num_outputs; ++i) {
     ret->out_types.emplace_back(out_array[i]->storage_type());
   }
   *out_stypes = dmlc::BeginPtr(ret->out_types);
   API_END();
 }

 int MXAutogradIsTraining(bool* curr) {
   API_BEGIN();
   *curr = Imperative::Get()->is_training();
   API_END();
 }

 int MXAutogradSetIsTraining(int is_training, int* prev) {
   API_BEGIN();
   *prev = Imperative::Get()->set_is_training(static_cast<bool>(is_training));
   API_END();
 }

 int MXAutogradIsRecording(bool* curr) {
   API_BEGIN();
   *curr = Imperative::Get()->is_recording();
   API_END();
 }

 int MXAutogradSetIsRecording(int is_recording, int* prev) {
   API_BEGIN();
   *prev = Imperative::Get()->set_is_recording(static_cast<bool>(is_recording));
   API_END();
 }

 int MXAutogradMarkVariables(mx_uint num_var,
                             NDArrayHandle *var_handles,
                             mx_uint *reqs_array,
                             NDArrayHandle *grad_handles) {
   API_BEGIN();
   std::vector<NDArray*> variables, gradients;
   std::vector<mx_uint> grad_reqs;
   variables.reserve(num_var);
   gradients.reserve(num_var);
   grad_reqs.reserve(num_var);
   for (mx_uint i = 0; i < num_var; ++i) {
     variables.emplace_back(static_cast<NDArray*>(var_handles[i]));
     gradients.emplace_back(static_cast<NDArray*>(grad_handles[i]));
     grad_reqs.emplace_back(reqs_array[i]);
   }
   Imperative::Get()->MarkVariables(variables, grad_reqs, gradients);
   API_END();
 }

 int MXAutogradComputeGradient(mx_uint num_output,
                               NDArrayHandle *output_handles) {
   return MXAutogradBackward(num_output, output_handles, nullptr, 0);
 }

 int MXAutogradBackward(mx_uint num_output,
                        NDArrayHandle *output_handles,
                        NDArrayHandle *ograd_handles,
                        int retain_graph) {
   return MXAutogradBackwardEx(num_output, output_handles, ograd_handles,
                               0, nullptr, retain_graph, false, true,
                               nullptr, nullptr);
 }

 int MXAutogradBackwardEx(mx_uint num_output,
                          NDArrayHandle *output_handles,
                          NDArrayHandle *ograd_handles,
                          mx_uint num_variables,
                          NDArrayHandle *var_handles,
                          int retain_graph,
                          int create_graph,
                          int is_train,
                          NDArrayHandle **grad_handles,
                          int **grad_stypes) {
   MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();
   API_BEGIN();

   std::vector<NDArray*> outputs, ograds, variables;
   outputs.reserve(num_output);
   for (mx_uint i = 0; i < num_output; ++i) {
     outputs.emplace_back(reinterpret_cast<NDArray*>(output_handles[i]));
   }

   ograds.reserve(num_output);
   for (mx_uint i = 0; i < num_output; ++i) {
     if (ograd_handles != nullptr) {
       ograds.emplace_back(reinterpret_cast<NDArray*>(ograd_handles[i]));
     } else {
       ograds.emplace_back(nullptr);
     }
   }

   variables.reserve(num_variables);
   for (mx_uint i = 0; i < num_variables; ++i) {
     variables.emplace_back(reinterpret_cast<NDArray*>(var_handles[i]));
   }

   auto grads = Imperative::Get()->Backward(outputs, ograds, variables, is_train,
                                                   retain_graph, create_graph);
   if (num_variables != 0) {
     ret->ret_handles.clear();
     ret->out_types.clear();
     ret->ret_handles.reserve(grads.size());
     ret->out_types.reserve(grads.size());
     for (const auto& i : grads) {
       ret->ret_handles.push_back(i);
       ret->out_types.push_back(i->storage_type());
     }
     *grad_handles = dmlc::BeginPtr(ret->ret_handles);
     *grad_stypes = dmlc::BeginPtr(ret->out_types);
   }
   API_END();
 }

 int MXAutogradGetSymbol(NDArrayHandle handle, SymbolHandle *out) {
   API_BEGIN();
   NDArray *head = reinterpret_cast<NDArray*>(handle);
   auto sym = new nnvm::Symbol(head->get_autograd_symbol());
   *out = reinterpret_cast<SymbolHandle>(sym);
   API_END();
 }
	/*
	* Licensed to the Apache Software Foundation (ASF) under one
	* or more contributor license agreements. See the NOTICE file
	* distributed with this work for additional information
	* regarding copyright ownership. The ASF licenses this file
	* to you under the Apache License, Version 2.0 (the
	* "License"); you may not use this file except in compliance
	* with the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing,
	* software distributed under the License is distributed on an
	* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
	* KIND, either express or implied. See the License for the
	* specific language governing permissions and limitations
	* under the License.
	*/

	/*!
	* Copyright (c) 2016 by Contributors
	* \file c_api_ndarray.cc
	* \brief C API of mxnet
	*/

	#include <mxnet/base.h>
	#include <mxnet/c_api.h>
	#include <mxnet/operator.h>
	#include <mxnet/operator_util.h>
	#include <mxnet/op_attr_types.h>
	#include <mxnet/imperative.h>
	#include <nnvm/node.h>
	#include <nnvm/op_attr_types.h>
	#include <string>
	#include "./c_api_common.h"
	#include "../common/utils.h"
	#include "../common/exec_utils.h"
	#include "../imperative/imperative_utils.h"
	#include "../imperative/cached_op.h"

	using namespace mxnet;

	void SetNDInputsOutputs(const nnvm::Op* op,
	std::vector<NDArray> ndinputs,
	std::vector<NDArray> ndoutputs,
	int num_inputs,
	const NDArrayHandle *inputs,
	int *num_outputs,
	int infered_num_outputs,
	int num_visible_outputs,
	NDArrayHandle **outputs) {
	NDArray** out_array = reinterpret_cast<NDArray**>(outputs);

	ndinputs->clear();
	ndinputs->reserve(num_inputs);
	for (int i = 0; i < num_inputs; ++i) {
	ndinputs->emplace_back(reinterpret_cast<NDArray*>(inputs[i]));
	}

	ndoutputs->clear();
	ndoutputs->reserve(infered_num_outputs);
	if (out_array == nullptr) {
	for (int i = 0; i < infered_num_outputs; ++i) {
	ndoutputs->emplace_back(new NDArray());
	}
	*num_outputs = num_visible_outputs;
	} else {
	CHECK(num_outputs == infered_num_outputs \|\| num_outputs == num_visible_outputs)
	<< "Operator expects " << infered_num_outputs << " (all) or "
	<< num_visible_outputs << " (visible only) outputs, but got "
	<< *num_outputs << " instead.";
	for (int i = 0; i < *num_outputs; ++i) {
	ndoutputs->emplace_back(out_array[i]);
	}
	for (int i = *num_outputs; i < infered_num_outputs; ++i) {
	ndoutputs->emplace_back(new NDArray());
	}
	}
	}

	void MXImperativeInvokeImpl(AtomicSymbolCreator creator,
	int num_inputs,
	NDArrayHandle *inputs,
	int *num_outputs,
	NDArrayHandle **outputs,
	int num_params,
	const char **param_keys,
	const char **param_vals) {
	const nnvm::Op* op = static_cast<nnvm::Op*>(creator);
	MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();

	nnvm::NodeAttrs attrs = imperative::ParseAttrs(op, num_inputs, num_params,
	param_keys, param_vals);

	int infered_num_outputs;
	int num_visible_outputs;
	imperative::SetNumOutputs(op, attrs, num_inputs, &infered_num_outputs, &num_visible_outputs);

	std::vector<NDArray*> ndinputs, ndoutputs;
	SetNDInputsOutputs(op, &ndinputs, &ndoutputs, num_inputs, inputs,
	num_outputs, infered_num_outputs, num_visible_outputs, outputs);

	auto state = Imperative::Get()->Invoke(Context::CPU(), attrs, ndinputs, ndoutputs);
	if (Imperative::Get()->is_recording()) {
	Imperative::Get()->RecordOp(std::move(attrs), ndinputs, ndoutputs, state);
	}

	for (int i = *num_outputs; i < infered_num_outputs; ++i) delete ndoutputs[i];

	if (*outputs == nullptr) {
	ret->ret_handles.clear();
	ret->ret_handles.reserve(*num_outputs);
	for (int i = 0; i < *num_outputs; ++i) ret->ret_handles.push_back(ndoutputs[i]);
	outputs = reinterpret_cast<NDArrayHandle>(dmlc::BeginPtr(ret->ret_handles));
	}
	}

	int MXImperativeInvoke(AtomicSymbolCreator creator,
	int num_inputs,
	NDArrayHandle *inputs,
	int *num_outputs,
	NDArrayHandle **outputs,
	int num_params,
	const char **param_keys,
	const char **param_vals) {
	API_BEGIN();
	MXImperativeInvokeImpl(creator, num_inputs, inputs, num_outputs, outputs,
	num_params, param_keys, param_vals);
	API_END();
	}

	int MXImperativeInvokeEx(AtomicSymbolCreator creator,
	int num_inputs,
	NDArrayHandle *inputs,
	int *num_outputs,
	NDArrayHandle **outputs,
	int num_params,
	const char **param_keys,
	const char **param_vals,
	const int **out_stypes) { // outputs storage types
	MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();
	API_BEGIN();
	MXImperativeInvokeImpl(creator, num_inputs, inputs, num_outputs, outputs,
	num_params, param_keys, param_vals);
	NDArray** out_array = reinterpret_cast<NDArray**>(outputs);
	ret->out_types.clear();
	ret->out_types.reserve(*num_outputs);
	for (int i = 0; i < *num_outputs; ++i) {
	ret->out_types.emplace_back(out_array[i]->storage_type());
	}
	*out_stypes = dmlc::BeginPtr(ret->out_types);
	API_END();
	}

	int MXCreateCachedOp(SymbolHandle handle,
	CachedOpHandle *out) {
	nnvm::Symbol* sym = static_cast<nnvm::Symbol*>(handle);

	API_BEGIN();
	auto inputs = sym->ListInputs(nnvm::Symbol::kAll);
	std::vector<std::string> input_names;
	input_names.reserve(inputs.size());
	for (const auto& i : inputs) input_names.push_back(i->attrs.name);
	*out = new CachedOpPtr(new CachedOp(
	*sym, std::vector<std::pair<std::string, std::string> >()));
	API_END();
	}

	int MXCreateCachedOpEx(SymbolHandle handle,
	int num_flags,
	const char** keys,
	const char** vals,
	CachedOpHandle *out) {
	nnvm::Symbol* sym = static_cast<nnvm::Symbol*>(handle);

	API_BEGIN();
	std::vector<std::pair<std::string, std::string> > flags;
	for (int i = 0; i < num_flags; ++i) {
	flags.push_back({keys[i], vals[i]});
	}
	out = new CachedOpPtr(new CachedOp(sym, flags));
	API_END();
	}

	int MXFreeCachedOp(CachedOpHandle handle) {
	CachedOpPtr* g = static_cast<CachedOpPtr*>(handle);
	API_BEGIN();
	delete g;
	API_END();
	}

	int MXInvokeCachedOp(CachedOpHandle handle,
	int num_inputs,
	NDArrayHandle *inputs,
	int *num_outputs,
	NDArrayHandle **outputs) {
	MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();

	API_BEGIN();
	CachedOpPtr op = static_cast<CachedOpPtr>(handle);
	std::vector<NDArray*> ndinputs;
	ndinputs.reserve(num_inputs);
	for (int i = 0; i < num_inputs; ++i) {
	ndinputs.push_back(reinterpret_cast<NDArray*>(inputs[i]));
	}

	std::vector<NDArray*> ndoutputs;
	ndoutputs.reserve(op->num_outputs());
	if (*outputs == nullptr) {
	*num_outputs = op->num_outputs();
	for (int i = 0; i < *num_outputs; ++i) ndoutputs.push_back(new NDArray());
	} else {
	CHECK_EQ(*num_outputs, op->num_outputs())
	<< "CachedOp expects " << op->num_outputs() << " outputs, but "
	<< *num_outputs << " was given.";
	for (int i = 0; i < *num_outputs; ++i) {
	ndoutputs.push_back(reinterpret_cast<NDArray>((outputs)[i]));
	}
	}

	op->Forward(op, ndinputs, ndoutputs);

	if (*outputs == nullptr) {
	ret->ret_handles.clear();
	ret->ret_handles.reserve(*num_outputs);
	for (int i = 0; i < *num_outputs; ++i) {
	ret->ret_handles.push_back(ndoutputs[i]);
	}
	*outputs = dmlc::BeginPtr(ret->ret_handles);
	}

	API_END();
	}

	int MXInvokeCachedOpEx(CachedOpHandle handle,
	int num_inputs,
	NDArrayHandle *inputs,
	int *num_outputs,
	NDArrayHandle **outputs,
	const int **out_stypes) { // outputs storage types
	MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();
	int err = MXInvokeCachedOp(handle, num_inputs, inputs, num_outputs, outputs);
	if (err != 0) return err;
	API_BEGIN();
	NDArray out_array = reinterpret_cast<NDArray>(*outputs);
	ret->out_types.clear();
	ret->out_types.reserve(*num_outputs);
	for (int i = 0; i < *num_outputs; ++i) {
	ret->out_types.emplace_back(out_array[i]->storage_type());
	}
	*out_stypes = dmlc::BeginPtr(ret->out_types);
	API_END();
	}

	int MXAutogradIsTraining(bool* curr) {
	API_BEGIN();
	*curr = Imperative::Get()->is_training();
	API_END();
	}

	int MXAutogradSetIsTraining(int is_training, int* prev) {
	API_BEGIN();
	*prev = Imperative::Get()->set_is_training(static_cast<bool>(is_training));
	API_END();
	}

	int MXAutogradIsRecording(bool* curr) {
	API_BEGIN();
	*curr = Imperative::Get()->is_recording();
	API_END();
	}

	int MXAutogradSetIsRecording(int is_recording, int* prev) {
	API_BEGIN();
	*prev = Imperative::Get()->set_is_recording(static_cast<bool>(is_recording));
	API_END();
	}

	int MXAutogradMarkVariables(mx_uint num_var,
	NDArrayHandle *var_handles,
	mx_uint *reqs_array,
	NDArrayHandle *grad_handles) {
	API_BEGIN();
	std::vector<NDArray*> variables, gradients;
	std::vector<mx_uint> grad_reqs;
	variables.reserve(num_var);
	gradients.reserve(num_var);
	grad_reqs.reserve(num_var);
	for (mx_uint i = 0; i < num_var; ++i) {
	variables.emplace_back(static_cast<NDArray*>(var_handles[i]));
	gradients.emplace_back(static_cast<NDArray*>(grad_handles[i]));
	grad_reqs.emplace_back(reqs_array[i]);
	}
	Imperative::Get()->MarkVariables(variables, grad_reqs, gradients);
	API_END();
	}

	int MXAutogradComputeGradient(mx_uint num_output,
	NDArrayHandle *output_handles) {
	return MXAutogradBackward(num_output, output_handles, nullptr, 0);
	}

	int MXAutogradBackward(mx_uint num_output,
	NDArrayHandle *output_handles,
	NDArrayHandle *ograd_handles,
	int retain_graph) {
	return MXAutogradBackwardEx(num_output, output_handles, ograd_handles,
	0, nullptr, retain_graph, false, true,
	nullptr, nullptr);
	}

	int MXAutogradBackwardEx(mx_uint num_output,
	NDArrayHandle *output_handles,
	NDArrayHandle *ograd_handles,
	mx_uint num_variables,
	NDArrayHandle *var_handles,
	int retain_graph,
	int create_graph,
	int is_train,
	NDArrayHandle **grad_handles,
	int **grad_stypes) {
	MXAPIThreadLocalEntry *ret = MXAPIThreadLocalStore::Get();
	API_BEGIN();

	std::vector<NDArray*> outputs, ograds, variables;
	outputs.reserve(num_output);
	for (mx_uint i = 0; i < num_output; ++i) {
	outputs.emplace_back(reinterpret_cast<NDArray*>(output_handles[i]));
	}

	ograds.reserve(num_output);
	for (mx_uint i = 0; i < num_output; ++i) {
	if (ograd_handles != nullptr) {
	ograds.emplace_back(reinterpret_cast<NDArray*>(ograd_handles[i]));
	} else {
	ograds.emplace_back(nullptr);
	}
	}

	variables.reserve(num_variables);
	for (mx_uint i = 0; i < num_variables; ++i) {
	variables.emplace_back(reinterpret_cast<NDArray*>(var_handles[i]));
	}

	auto grads = Imperative::Get()->Backward(outputs, ograds, variables, is_train,
	retain_graph, create_graph);
	if (num_variables != 0) {
	ret->ret_handles.clear();
	ret->out_types.clear();
	ret->ret_handles.reserve(grads.size());
	ret->out_types.reserve(grads.size());
	for (const auto& i : grads) {
	ret->ret_handles.push_back(i);
	ret->out_types.push_back(i->storage_type());
	}
	*grad_handles = dmlc::BeginPtr(ret->ret_handles);
	*grad_stypes = dmlc::BeginPtr(ret->out_types);
	}
	API_END();
	}

	int MXAutogradGetSymbol(NDArrayHandle handle, SymbolHandle *out) {
	API_BEGIN();
	NDArray head = reinterpret_cast<NDArray>(handle);
	auto sym = new nnvm::Symbol(head->get_autograd_symbol());
	*out = reinterpret_cast<SymbolHandle>(sym);
	API_END();
	}