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<h1>Source code for mxnet.autograd</h1><div class="highlight"><pre>
<span></span><span class="c1"># Licensed to the Apache Software Foundation (ASF) under one</span>
<span class="c1"># or more contributor license agreements. See the NOTICE file</span>
<span class="c1"># distributed with this work for additional information</span>
<span class="c1"># regarding copyright ownership. The ASF licenses this file</span>
<span class="c1"># to you under the Apache License, Version 2.0 (the</span>
<span class="c1"># "License"); you may not use this file except in compliance</span>
<span class="c1"># with the License. You may obtain a copy of the License at</span>
<span class="c1">#</span>
<span class="c1"># http://www.apache.org/licenses/LICENSE-2.0</span>
<span class="c1">#</span>
<span class="c1"># Unless required by applicable law or agreed to in writing,</span>
<span class="c1"># software distributed under the License is distributed on an</span>
<span class="c1"># "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY</span>
<span class="c1"># KIND, either express or implied. See the License for the</span>
<span class="c1"># specific language governing permissions and limitations</span>
<span class="c1"># under the License.</span>
<span class="c1"># coding: utf-8</span>
<span class="sd">"""Autograd for NDArray."""</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="k">import</span> <span class="n">absolute_import</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="k">import</span> <span class="n">division</span>
<span class="kn">from</span> <span class="nn">array</span> <span class="k">import</span> <span class="n">array</span>
<span class="kn">from</span> <span class="nn">threading</span> <span class="k">import</span> <span class="n">Lock</span>
<span class="kn">import</span> <span class="nn">traceback</span>
<span class="kn">import</span> <span class="nn">ctypes</span>
<span class="kn">from</span> <span class="nn">ctypes</span> <span class="k">import</span> <span class="n">c_int</span><span class="p">,</span> <span class="n">c_void_p</span><span class="p">,</span> <span class="n">CFUNCTYPE</span><span class="p">,</span> <span class="n">POINTER</span><span class="p">,</span> <span class="n">cast</span>
<span class="kn">from</span> <span class="nn">.base</span> <span class="k">import</span> <span class="n">_LIB</span><span class="p">,</span> <span class="n">check_call</span><span class="p">,</span> <span class="n">string_types</span><span class="p">,</span> <span class="n">mx_uint</span>
<span class="kn">from</span> <span class="nn">.base</span> <span class="k">import</span> <span class="n">NDArrayHandle</span><span class="p">,</span> <span class="n">c_array</span><span class="p">,</span> <span class="n">c_handle_array</span><span class="p">,</span> <span class="n">c_array_buf</span><span class="p">,</span> <span class="n">MXCallbackList</span><span class="p">,</span> <span class="n">SymbolHandle</span>
<span class="kn">from</span> <span class="nn">.ndarray</span> <span class="k">import</span> <span class="n">NDArray</span><span class="p">,</span> <span class="n">_ndarray_cls</span>
<span class="kn">from</span> <span class="nn">.ndarray</span> <span class="k">import</span> <span class="n">_GRAD_REQ_MAP</span>
<span class="kn">from</span> <span class="nn">.symbol</span> <span class="k">import</span> <span class="n">Symbol</span>
<div class="viewcode-block" id="set_recording"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.set_recording">[docs]</a><span class="k">def</span> <span class="nf">set_recording</span><span class="p">(</span><span class="n">is_recording</span><span class="p">):</span> <span class="c1">#pylint: disable=redefined-outer-name</span>
<span class="sd">"""Set status to recording/not recording. When recording, graph will be constructed</span>
<span class="sd"> for gradient computation.</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> is_recording: bool</span>
<span class="sd"> Returns</span>
<span class="sd"> -------</span>
<span class="sd"> previous state before this set.</span>
<span class="sd"> """</span>
<span class="n">prev</span> <span class="o">=</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">()</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradSetIsRecording</span><span class="p">(</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="n">is_recording</span><span class="p">),</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">prev</span><span class="p">)))</span>
<span class="k">return</span> <span class="nb">bool</span><span class="p">(</span><span class="n">prev</span><span class="o">.</span><span class="n">value</span><span class="p">)</span></div>
<div class="viewcode-block" id="set_training"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.set_training">[docs]</a><span class="k">def</span> <span class="nf">set_training</span><span class="p">(</span><span class="n">train_mode</span><span class="p">):</span> <span class="c1">#pylint: disable=redefined-outer-name</span>
<span class="sd">"""Set status to training/predicting. This affects ctx.is_train in operator</span>
<span class="sd"> running context. For example, Dropout will drop inputs randomly when</span>
<span class="sd"> train_mode=True while simply passing through if train_mode=False.</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> train_mode: bool</span>
<span class="sd"> Returns</span>
<span class="sd"> -------</span>
<span class="sd"> previous state before this set.</span>
<span class="sd"> """</span>
<span class="n">prev</span> <span class="o">=</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">()</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradSetIsTraining</span><span class="p">(</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="n">train_mode</span><span class="p">),</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">prev</span><span class="p">)))</span>
<span class="k">return</span> <span class="nb">bool</span><span class="p">(</span><span class="n">prev</span><span class="o">.</span><span class="n">value</span><span class="p">)</span></div>
<div class="viewcode-block" id="is_recording"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.is_recording">[docs]</a><span class="k">def</span> <span class="nf">is_recording</span><span class="p">():</span>
<span class="sd">"""Get status on recording/not recording.</span>
<span class="sd"> Returns</span>
<span class="sd"> -------</span>
<span class="sd"> Current state of recording.</span>
<span class="sd"> """</span>
<span class="n">curr</span> <span class="o">=</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">c_bool</span><span class="p">()</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradIsRecording</span><span class="p">(</span><span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">curr</span><span class="p">)))</span>
<span class="k">return</span> <span class="n">curr</span><span class="o">.</span><span class="n">value</span></div>
<div class="viewcode-block" id="is_training"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.is_training">[docs]</a><span class="k">def</span> <span class="nf">is_training</span><span class="p">():</span>
<span class="sd">"""Get status on training/predicting.</span>
<span class="sd"> Returns</span>
<span class="sd"> -------</span>
<span class="sd"> Current state of training/predicting.</span>
<span class="sd"> """</span>
<span class="n">curr</span> <span class="o">=</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">c_bool</span><span class="p">()</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradIsTraining</span><span class="p">(</span><span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">curr</span><span class="p">)))</span>
<span class="k">return</span> <span class="n">curr</span><span class="o">.</span><span class="n">value</span></div>
<span class="k">class</span> <span class="nc">_RecordingStateScope</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="sd">"""Scope for managing training state.</span>
<span class="sd"> Example::</span>
<span class="sd"> with _RecordingStateScope(True, True):</span>
<span class="sd"> y = model(x)</span>
<span class="sd"> backward([y])</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">is_record</span><span class="p">,</span> <span class="n">train_mode</span><span class="p">):</span> <span class="c1">#pylint: disable=redefined-outer-name</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_enter_is_record</span> <span class="o">=</span> <span class="n">is_record</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_enter_train_mode</span> <span class="o">=</span> <span class="n">train_mode</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_prev_is_record</span> <span class="o">=</span> <span class="kc">None</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_prev_train_mode</span> <span class="o">=</span> <span class="kc">None</span>
<span class="k">def</span> <span class="nf">__enter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">_enter_is_record</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_prev_is_record</span> <span class="o">=</span> <span class="n">set_recording</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_enter_is_record</span><span class="p">)</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">_enter_train_mode</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_prev_train_mode</span> <span class="o">=</span> <span class="n">set_training</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_enter_train_mode</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">__exit__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">ptype</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">trace</span><span class="p">):</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">_enter_is_record</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span> <span class="ow">and</span> <span class="bp">self</span><span class="o">.</span><span class="n">_prev_is_record</span> <span class="o">!=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_enter_is_record</span><span class="p">:</span>
<span class="n">set_recording</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_prev_is_record</span><span class="p">)</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">_enter_train_mode</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span> <span class="ow">and</span> <span class="bp">self</span><span class="o">.</span><span class="n">_prev_train_mode</span> <span class="o">!=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_enter_train_mode</span><span class="p">:</span>
<span class="n">set_training</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_prev_train_mode</span><span class="p">)</span>
<div class="viewcode-block" id="record"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.record">[docs]</a><span class="k">def</span> <span class="nf">record</span><span class="p">(</span><span class="n">train_mode</span><span class="o">=</span><span class="kc">True</span><span class="p">):</span> <span class="c1">#pylint: disable=redefined-outer-name</span>
<span class="sd">"""Returns an autograd recording scope context to be used in 'with' statement</span>
<span class="sd"> and captures code that needs gradients to be calculated.</span>
<span class="sd"> .. note:: When forwarding with train_mode=False, the corresponding backward</span>
<span class="sd"> should also use train_mode=False, otherwise gradient is undefined.</span>
<span class="sd"> Example::</span>
<span class="sd"> with autograd.record():</span>
<span class="sd"> y = model(x)</span>
<span class="sd"> backward([y])</span>
<span class="sd"> metric.update(...)</span>
<span class="sd"> optim.step(...)</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> train_mode: bool, default True</span>
<span class="sd"> Whether the forward pass is in training or predicting mode. This controls the behavior</span>
<span class="sd"> of some layers such as Dropout, BatchNorm.</span>
<span class="sd"> """</span>
<span class="k">return</span> <span class="n">_RecordingStateScope</span><span class="p">(</span><span class="kc">True</span><span class="p">,</span> <span class="n">train_mode</span><span class="p">)</span></div>
<div class="viewcode-block" id="pause"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.pause">[docs]</a><span class="k">def</span> <span class="nf">pause</span><span class="p">(</span><span class="n">train_mode</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span> <span class="c1">#pylint: disable=redefined-outer-name</span>
<span class="sd">"""Returns a scope context to be used in 'with' statement for codes that do not need</span>
<span class="sd"> gradients to be calculated.</span>
<span class="sd"> Example::</span>
<span class="sd"> with autograd.record():</span>
<span class="sd"> y = model(x)</span>
<span class="sd"> backward([y])</span>
<span class="sd"> with autograd.pause():</span>
<span class="sd"> # testing, IO, gradient updates...</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> train_mode: bool, default False</span>
<span class="sd"> Whether to do forward for training or predicting.</span>
<span class="sd"> """</span>
<span class="k">return</span> <span class="n">_RecordingStateScope</span><span class="p">(</span><span class="kc">False</span><span class="p">,</span> <span class="n">train_mode</span><span class="p">)</span></div>
<div class="viewcode-block" id="train_mode"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.train_mode">[docs]</a><span class="k">def</span> <span class="nf">train_mode</span><span class="p">():</span>
<span class="sd">"""Returns a scope context to be used in 'with' statement</span>
<span class="sd"> in which forward pass behavior is set to training mode,</span>
<span class="sd"> without changing the recording states.</span>
<span class="sd"> Example::</span>
<span class="sd"> y = model(x)</span>
<span class="sd"> with autograd.train_mode():</span>
<span class="sd"> y = dropout(y)</span>
<span class="sd"> """</span>
<span class="k">return</span> <span class="n">_RecordingStateScope</span><span class="p">(</span><span class="kc">None</span><span class="p">,</span> <span class="kc">True</span><span class="p">)</span></div>
<div class="viewcode-block" id="predict_mode"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.predict_mode">[docs]</a><span class="k">def</span> <span class="nf">predict_mode</span><span class="p">():</span>
<span class="sd">"""Returns a scope context to be used in 'with' statement</span>
<span class="sd"> in which forward pass behavior is set to inference mode,</span>
<span class="sd"> without changing the recording states.</span>
<span class="sd"> Example::</span>
<span class="sd"> with autograd.record():</span>
<span class="sd"> y = model(x)</span>
<span class="sd"> with autograd.predict_mode():</span>
<span class="sd"> y = sampling(y)</span>
<span class="sd"> backward([y])</span>
<span class="sd"> """</span>
<span class="k">return</span> <span class="n">_RecordingStateScope</span><span class="p">(</span><span class="kc">None</span><span class="p">,</span> <span class="kc">False</span><span class="p">)</span></div>
<div class="viewcode-block" id="mark_variables"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.mark_variables">[docs]</a><span class="k">def</span> <span class="nf">mark_variables</span><span class="p">(</span><span class="n">variables</span><span class="p">,</span> <span class="n">gradients</span><span class="p">,</span> <span class="n">grad_reqs</span><span class="o">=</span><span class="s1">'write'</span><span class="p">):</span>
<span class="sd">"""Mark NDArrays as variables to compute gradient for autograd.</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> variables: NDArray or list of NDArray</span>
<span class="sd"> gradients: NDArray or list of NDArray</span>
<span class="sd"> grad_reqs: str or list of str</span>
<span class="sd"> """</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">variables</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">):</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">gradients</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">)</span>
<span class="n">variables</span> <span class="o">=</span> <span class="p">[</span><span class="n">variables</span><span class="p">]</span>
<span class="n">gradients</span> <span class="o">=</span> <span class="p">[</span><span class="n">gradients</span><span class="p">]</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">grad_reqs</span><span class="p">,</span> <span class="n">string_types</span><span class="p">):</span>
<span class="n">grad_reqs</span> <span class="o">=</span> <span class="p">[</span><span class="n">_GRAD_REQ_MAP</span><span class="p">[</span><span class="n">grad_reqs</span><span class="p">]]</span><span class="o">*</span><span class="nb">len</span><span class="p">(</span><span class="n">variables</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">grad_reqs</span> <span class="o">=</span> <span class="p">[</span><span class="n">_GRAD_REQ_MAP</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">grad_reqs</span><span class="p">]</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradMarkVariables</span><span class="p">(</span>
<span class="nb">len</span><span class="p">(</span><span class="n">variables</span><span class="p">),</span>
<span class="n">c_handle_array</span><span class="p">(</span><span class="n">variables</span><span class="p">),</span>
<span class="n">c_array_buf</span><span class="p">(</span><span class="n">mx_uint</span><span class="p">,</span> <span class="n">array</span><span class="p">(</span><span class="s1">'I'</span><span class="p">,</span> <span class="n">grad_reqs</span><span class="p">)),</span>
<span class="n">c_handle_array</span><span class="p">(</span><span class="n">gradients</span><span class="p">)))</span></div>
<span class="k">def</span> <span class="nf">_parse_head</span><span class="p">(</span><span class="n">heads</span><span class="p">,</span> <span class="n">head_grads</span><span class="p">):</span>
<span class="sd">"""parse head gradient for backward and grad."""</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">heads</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">):</span>
<span class="n">heads</span> <span class="o">=</span> <span class="p">[</span><span class="n">heads</span><span class="p">]</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">head_grads</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">):</span>
<span class="n">head_grads</span> <span class="o">=</span> <span class="p">[</span><span class="n">head_grads</span><span class="p">]</span>
<span class="n">head_handles</span> <span class="o">=</span> <span class="n">c_handle_array</span><span class="p">(</span><span class="n">heads</span><span class="p">)</span>
<span class="k">if</span> <span class="n">head_grads</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="n">hgrad_handles</span> <span class="o">=</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">c_void_p</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">heads</span><span class="p">)</span> <span class="o">==</span> <span class="nb">len</span><span class="p">(</span><span class="n">head_grads</span><span class="p">),</span> \
<span class="s2">"heads and head_grads must be lists of the same length"</span>
<span class="n">hgrad_handles</span> <span class="o">=</span> <span class="n">c_array</span><span class="p">(</span><span class="n">NDArrayHandle</span><span class="p">,</span>
<span class="p">[</span><span class="n">i</span><span class="o">.</span><span class="n">handle</span> <span class="k">if</span> <span class="n">i</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span> <span class="k">else</span> <span class="n">NDArrayHandle</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">head_grads</span><span class="p">])</span>
<span class="k">return</span> <span class="n">head_handles</span><span class="p">,</span> <span class="n">hgrad_handles</span>
<div class="viewcode-block" id="backward"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.backward">[docs]</a><span class="k">def</span> <span class="nf">backward</span><span class="p">(</span><span class="n">heads</span><span class="p">,</span> <span class="n">head_grads</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">retain_graph</span><span class="o">=</span><span class="kc">False</span><span class="p">,</span> <span class="n">train_mode</span><span class="o">=</span><span class="kc">True</span><span class="p">):</span> <span class="c1">#pylint: disable=redefined-outer-name</span>
<span class="sd">"""Compute the gradients of heads w.r.t previously marked variables.</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> heads: NDArray or list of NDArray</span>
<span class="sd"> Output NDArray(s)</span>
<span class="sd"> head_grads: NDArray or list of NDArray or None</span>
<span class="sd"> Gradients with respect to heads.</span>
<span class="sd"> train_mode: bool, optional</span>
<span class="sd"> Whether to do backward for training or predicting.</span>
<span class="sd"> """</span>
<span class="n">head_handles</span><span class="p">,</span> <span class="n">hgrad_handles</span> <span class="o">=</span> <span class="n">_parse_head</span><span class="p">(</span><span class="n">heads</span><span class="p">,</span> <span class="n">head_grads</span><span class="p">)</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradBackwardEx</span><span class="p">(</span>
<span class="nb">len</span><span class="p">(</span><span class="n">head_handles</span><span class="p">),</span>
<span class="n">head_handles</span><span class="p">,</span>
<span class="n">hgrad_handles</span><span class="p">,</span>
<span class="mi">0</span><span class="p">,</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_void_p</span><span class="p">(</span><span class="mi">0</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="n">retain_graph</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="mi">0</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="n">train_mode</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_void_p</span><span class="p">(</span><span class="mi">0</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_void_p</span><span class="p">(</span><span class="mi">0</span><span class="p">)))</span></div>
<div class="viewcode-block" id="grad"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.grad">[docs]</a><span class="k">def</span> <span class="nf">grad</span><span class="p">(</span><span class="n">heads</span><span class="p">,</span> <span class="n">variables</span><span class="p">,</span> <span class="n">head_grads</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">retain_graph</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">create_graph</span><span class="o">=</span><span class="kc">False</span><span class="p">,</span>
<span class="n">train_mode</span><span class="o">=</span><span class="kc">True</span><span class="p">):</span> <span class="c1">#pylint: disable=redefined-outer-name</span>
<span class="sd">"""Compute the gradients of heads w.r.t variables. Gradients will be</span>
<span class="sd"> returned as new NDArrays instead of stored into `variable.grad`.</span>
<span class="sd"> Supports recording gradient graph for computing higher order gradients.</span>
<span class="sd"> .. Note: Currently only a very limited set of operators support higher order</span>
<span class="sd"> gradients.</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> heads: NDArray or list of NDArray</span>
<span class="sd"> Output NDArray(s)</span>
<span class="sd"> variables: NDArray or list of NDArray</span>
<span class="sd"> Input variables to compute gradients for.</span>
<span class="sd"> head_grads: NDArray or list of NDArray or None</span>
<span class="sd"> Gradients with respect to heads.</span>
<span class="sd"> retain_graph: bool</span>
<span class="sd"> Whether to keep computation graph to differentiate again, instead</span>
<span class="sd"> of clearing history and release memory. Defaults to the same value</span>
<span class="sd"> as create_graph.</span>
<span class="sd"> create_graph: bool</span>
<span class="sd"> Whether to record gradient graph for computing higher order</span>
<span class="sd"> train_mode: bool, optional</span>
<span class="sd"> Whether to do backward for training or prediction.</span>
<span class="sd"> Returns</span>
<span class="sd"> -------</span>
<span class="sd"> NDArray or list of NDArray:</span>
<span class="sd"> Gradients with respect to variables.</span>
<span class="sd"> Examples</span>
<span class="sd"> --------</span>
<span class="sd"> >>> x = mx.nd.ones((1,))</span>
<span class="sd"> >>> x.attach_grad()</span>
<span class="sd"> >>> with mx.autograd.record():</span>
<span class="sd"> ... z = mx.nd.elemwise_add(mx.nd.exp(x), x)</span>
<span class="sd"> >>> dx = mx.autograd.grad(z, [x], create_graph=True)</span>
<span class="sd"> >>> dx.backward()</span>
<span class="sd"> >>> print(dx.grad)</span>
<span class="sd"> [</span>
<span class="sd"> [ 3.71828175]</span>
<span class="sd"> <NDArray 1 @cpu(0)>]</span>
<span class="sd"> """</span>
<span class="n">head_handles</span><span class="p">,</span> <span class="n">hgrad_handles</span> <span class="o">=</span> <span class="n">_parse_head</span><span class="p">(</span><span class="n">heads</span><span class="p">,</span> <span class="n">head_grads</span><span class="p">)</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">variables</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">):</span>
<span class="n">variables</span> <span class="o">=</span> <span class="p">[</span><span class="n">variables</span><span class="p">]</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">variables</span><span class="p">),</span> <span class="s2">"variables cannot be an empty list."</span>
<span class="n">var_handles</span> <span class="o">=</span> <span class="n">c_handle_array</span><span class="p">(</span><span class="n">variables</span><span class="p">)</span>
<span class="n">retain_graph</span> <span class="o">=</span> <span class="n">retain_graph</span> <span class="k">if</span> <span class="n">retain_graph</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span> <span class="k">else</span> <span class="n">create_graph</span>
<span class="n">grad_vars</span> <span class="o">=</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">POINTER</span><span class="p">(</span><span class="n">NDArrayHandle</span><span class="p">)()</span>
<span class="n">grad_stypes</span> <span class="o">=</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">POINTER</span><span class="p">(</span><span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">)()</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradBackwardEx</span><span class="p">(</span>
<span class="nb">len</span><span class="p">(</span><span class="n">head_handles</span><span class="p">),</span>
<span class="n">head_handles</span><span class="p">,</span>
<span class="n">hgrad_handles</span><span class="p">,</span>
<span class="nb">len</span><span class="p">(</span><span class="n">var_handles</span><span class="p">),</span>
<span class="n">var_handles</span><span class="p">,</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="n">retain_graph</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="n">create_graph</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">c_int</span><span class="p">(</span><span class="n">train_mode</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">grad_vars</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">grad_stypes</span><span class="p">)))</span>
<span class="n">ret</span> <span class="o">=</span> <span class="p">[</span><span class="n">_ndarray_cls</span><span class="p">(</span><span class="n">ctypes</span><span class="o">.</span><span class="n">cast</span><span class="p">(</span><span class="n">grad_vars</span><span class="p">[</span><span class="n">i</span><span class="p">],</span> <span class="n">NDArrayHandle</span><span class="p">),</span>
<span class="n">stype</span><span class="o">=</span><span class="n">grad_stypes</span><span class="p">[</span><span class="n">i</span><span class="p">])</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">var_handles</span><span class="p">))]</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">variables</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">):</span>
<span class="k">return</span> <span class="n">ret</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="k">return</span> <span class="n">ret</span></div>
<div class="viewcode-block" id="get_symbol"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.get_symbol">[docs]</a><span class="k">def</span> <span class="nf">get_symbol</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
<span class="sd">"""Retrieve recorded computation history as `Symbol`.</span>
<span class="sd"> Parameters</span>
<span class="sd"> ----------</span>
<span class="sd"> x : NDArray</span>
<span class="sd"> Array representing the head of computation graph.</span>
<span class="sd"> Returns</span>
<span class="sd"> -------</span>
<span class="sd"> Symbol</span>
<span class="sd"> The retrieved Symbol.</span>
<span class="sd"> """</span>
<span class="n">hdl</span> <span class="o">=</span> <span class="n">SymbolHandle</span><span class="p">()</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXAutogradGetSymbol</span><span class="p">(</span><span class="n">x</span><span class="o">.</span><span class="n">handle</span><span class="p">,</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">hdl</span><span class="p">)))</span>
<span class="k">return</span> <span class="n">Symbol</span><span class="p">(</span><span class="n">hdl</span><span class="p">)</span></div>
<div class="viewcode-block" id="Function"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.Function">[docs]</a><span class="k">class</span> <span class="nc">Function</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="sd">"""Customize differentiation in autograd.</span>
<span class="sd"> If you don't want to use the gradients computed by the default</span>
<span class="sd"> chain-rule, you can use Function to customize differentiation for</span>
<span class="sd"> computation. You define your computation in</span>
<span class="sd"> the forward method and provide the customized differentiation</span>
<span class="sd"> in the backward method. During gradient computation, autograd will</span>
<span class="sd"> use the user-defined backward function instead of the default chain-rule.</span>
<span class="sd"> You can also cast to numpy array and back for some operations in</span>
<span class="sd"> forward and backward.</span>
<span class="sd"> For example, a stable sigmoid function can be defined as::</span>
<span class="sd"> class sigmoid(mx.autograd.Function):</span>
<span class="sd"> def forward(self, x):</span>
<span class="sd"> y = 1 / (1 + mx.nd.exp(-x))</span>
<span class="sd"> self.save_for_backward(y)</span>
<span class="sd"> return y</span>
<span class="sd"> def backward(self, dy):</span>
<span class="sd"> # backward takes as many inputs as forward's return value,</span>
<span class="sd"> # and returns as many NDArrays as forward's arguments.</span>
<span class="sd"> y, = self.saved_tensors</span>
<span class="sd"> return dy * y * (1-y)</span>
<span class="sd"> Then, the function can be used in the following way::</span>
<span class="sd"> func = sigmoid()</span>
<span class="sd"> x = mx.nd.random.uniform(shape=(10,))</span>
<span class="sd"> x.attach_grad()</span>
<span class="sd"> with mx.autograd.record():</span>
<span class="sd"> m = func(x)</span>
<span class="sd"> m.backward()</span>
<span class="sd"> dx = x.grad.asnumpy()</span>
<span class="sd"> """</span>
<span class="n">_bwd_functype</span> <span class="o">=</span> <span class="n">CFUNCTYPE</span><span class="p">(</span><span class="n">c_int</span><span class="p">,</span> <span class="n">c_int</span><span class="p">,</span> <span class="n">c_int</span><span class="p">,</span> <span class="n">POINTER</span><span class="p">(</span><span class="n">c_void_p</span><span class="p">),</span>
<span class="n">POINTER</span><span class="p">(</span><span class="n">c_int</span><span class="p">),</span> <span class="n">c_int</span><span class="p">,</span> <span class="n">c_void_p</span><span class="p">)</span>
<span class="n">_del_functype</span> <span class="o">=</span> <span class="n">CFUNCTYPE</span><span class="p">(</span><span class="n">c_int</span><span class="p">,</span> <span class="n">c_void_p</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">_Registry</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="sd">"""CustomOp registry."""</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">ref_holder</span> <span class="o">=</span> <span class="p">{}</span>
<span class="bp">self</span><span class="o">.</span><span class="n">counter</span> <span class="o">=</span> <span class="mi">0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">lock</span> <span class="o">=</span> <span class="n">Lock</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">inc</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""Get index for new entry."""</span>
<span class="bp">self</span><span class="o">.</span><span class="n">lock</span><span class="o">.</span><span class="n">acquire</span><span class="p">()</span>
<span class="n">cur</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">counter</span>
<span class="bp">self</span><span class="o">.</span><span class="n">counter</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="bp">self</span><span class="o">.</span><span class="n">lock</span><span class="o">.</span><span class="n">release</span><span class="p">()</span>
<span class="k">return</span> <span class="n">cur</span>
<span class="n">_registry</span> <span class="o">=</span> <span class="n">_Registry</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_used</span> <span class="o">=</span> <span class="kc">False</span>
<span class="bp">self</span><span class="o">.</span><span class="n">saved_tensors</span> <span class="o">=</span> <span class="p">()</span>
<span class="k">def</span> <span class="nf">save_for_backward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">saved_tensors</span> <span class="o">=</span> <span class="n">args</span>
<span class="k">def</span> <span class="nf">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">inputs</span><span class="p">):</span>
<span class="k">assert</span> <span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">_used</span><span class="p">,</span> \
<span class="s2">"Each Function instance can only be called once. "</span>\
<span class="s2">"Please create another instance."</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_used</span> <span class="o">=</span> <span class="kc">True</span>
<span class="n">prev_recording</span> <span class="o">=</span> <span class="n">set_recording</span><span class="p">(</span><span class="kc">False</span><span class="p">)</span>
<span class="n">outputs</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">forward</span><span class="p">(</span><span class="o">*</span><span class="n">inputs</span><span class="p">)</span>
<span class="n">set_recording</span><span class="p">(</span><span class="n">prev_recording</span><span class="p">)</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">prev_recording</span><span class="p">:</span>
<span class="k">return</span> <span class="n">outputs</span>
<span class="n">ret_outputs</span> <span class="o">=</span> <span class="n">outputs</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">outputs</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">):</span>
<span class="n">outputs</span> <span class="o">=</span> <span class="p">(</span><span class="n">outputs</span><span class="p">,)</span>
<span class="n">key</span> <span class="o">=</span> <span class="n">Function</span><span class="o">.</span><span class="n">_registry</span><span class="o">.</span><span class="n">inc</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">backward_entry</span><span class="p">(</span><span class="n">num_ograds</span><span class="p">,</span> <span class="n">num_igrads</span><span class="p">,</span> <span class="n">ptrs</span><span class="p">,</span> <span class="n">reqs</span><span class="p">,</span> <span class="n">is_train</span><span class="p">,</span> <span class="n">_</span><span class="p">):</span>
<span class="sd">"""entry point for backward."""</span>
<span class="c1"># pylint: disable=W0613</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">output_grads</span> <span class="o">=</span> <span class="p">[</span><span class="n">NDArray</span><span class="p">(</span><span class="n">ctypes</span><span class="o">.</span><span class="n">cast</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">NDArrayHandle</span><span class="p">),</span> <span class="n">writable</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span> \
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">ptrs</span><span class="p">[:</span><span class="n">num_ograds</span><span class="p">]]</span>
<span class="n">input_grads</span> <span class="o">=</span> <span class="p">[</span><span class="n">NDArray</span><span class="p">(</span><span class="n">ctypes</span><span class="o">.</span><span class="n">cast</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">NDArrayHandle</span><span class="p">),</span> <span class="n">writable</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> \
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">ptrs</span><span class="p">[</span><span class="n">num_ograds</span><span class="p">:</span><span class="n">num_ograds</span><span class="o">+</span><span class="n">num_igrads</span><span class="p">]]</span>
<span class="n">reqs</span> <span class="o">=</span> <span class="p">[</span><span class="n">reqs</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">num_igrads</span><span class="p">)]</span>
<span class="n">rets</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">backward</span><span class="p">(</span><span class="o">*</span><span class="n">output_grads</span><span class="p">)</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">rets</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">):</span>
<span class="n">rets</span> <span class="o">=</span> <span class="p">(</span><span class="n">rets</span><span class="p">,)</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">rets</span><span class="p">)</span> <span class="o">==</span> <span class="nb">len</span><span class="p">(</span><span class="n">input_grads</span><span class="p">),</span> \
<span class="s2">"</span><span class="si">%s</span><span class="s2">.backward must return exactly the same number "</span> \
<span class="s2">"of NDArrays as the number of NDArrays arguments to forward."</span> \
<span class="s2">"Expecting </span><span class="si">%d</span><span class="s2"> got </span><span class="si">%d</span><span class="s2">"</span><span class="o">%</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span><span class="o">.</span><span class="n">name</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">input_grads</span><span class="p">),</span> <span class="nb">len</span><span class="p">(</span><span class="n">rets</span><span class="p">))</span>
<span class="k">for</span> <span class="n">igrad</span><span class="p">,</span> <span class="n">ret</span><span class="p">,</span> <span class="n">req</span> <span class="ow">in</span> <span class="nb">zip</span><span class="p">(</span><span class="n">input_grads</span><span class="p">,</span> <span class="n">rets</span><span class="p">,</span> <span class="n">reqs</span><span class="p">):</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">ret</span><span class="p">,</span> <span class="n">NDArray</span><span class="p">),</span> \
<span class="s2">"autograd.Function.backward must return NDArrays, not </span><span class="si">%s</span><span class="s2">"</span><span class="o">%</span><span class="nb">type</span><span class="p">(</span><span class="n">ret</span><span class="p">)</span>
<span class="k">if</span> <span class="n">req</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span> <span class="c1"># null</span>
<span class="k">return</span> <span class="kc">True</span>
<span class="k">elif</span> <span class="n">req</span> <span class="o">==</span> <span class="mi">1</span> <span class="ow">or</span> <span class="n">req</span> <span class="o">==</span> <span class="mi">2</span><span class="p">:</span> <span class="c1"># write or inplace</span>
<span class="n">igrad</span><span class="p">[:]</span> <span class="o">=</span> <span class="n">ret</span>
<span class="k">elif</span> <span class="n">req</span> <span class="o">==</span> <span class="s1">'add'</span><span class="p">:</span>
<span class="n">igrad</span><span class="p">[:]</span> <span class="o">+=</span> <span class="n">ret</span>
<span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span> <span class="c1"># pylint: disable=broad-except</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Error in Function.backward: </span><span class="si">%s</span><span class="s1">'</span> <span class="o">%</span> <span class="n">traceback</span><span class="o">.</span><span class="n">format_exc</span><span class="p">())</span>
<span class="k">return</span> <span class="kc">False</span>
<span class="k">return</span> <span class="kc">True</span>
<span class="k">def</span> <span class="nf">delete_entry</span><span class="p">(</span><span class="n">_</span><span class="p">):</span>
<span class="sd">"""C Callback for CustomFunction::delete"""</span>
<span class="k">try</span><span class="p">:</span>
<span class="k">del</span> <span class="n">Function</span><span class="o">.</span><span class="n">_registry</span><span class="o">.</span><span class="n">ref_holder</span><span class="p">[</span><span class="n">key</span><span class="p">]</span>
<span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span> <span class="c1"># pylint: disable=broad-except</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Error in autograd.Function.delete: </span><span class="si">%s</span><span class="s1">'</span> <span class="o">%</span> <span class="n">traceback</span><span class="o">.</span><span class="n">format_exc</span><span class="p">())</span>
<span class="k">return</span> <span class="kc">False</span>
<span class="k">return</span> <span class="kc">True</span>
<span class="n">callbacks</span> <span class="o">=</span> <span class="p">[</span><span class="n">Function</span><span class="o">.</span><span class="n">_bwd_functype</span><span class="p">(</span><span class="n">backward_entry</span><span class="p">),</span>
<span class="n">Function</span><span class="o">.</span><span class="n">_del_functype</span><span class="p">(</span><span class="n">delete_entry</span><span class="p">)]</span>
<span class="n">callbacks</span> <span class="o">=</span> <span class="p">[</span><span class="n">cast</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">CFUNCTYPE</span><span class="p">(</span><span class="n">c_int</span><span class="p">))</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">callbacks</span><span class="p">]</span>
<span class="n">context</span> <span class="o">=</span> <span class="n">MXCallbackList</span><span class="p">(</span><span class="n">c_int</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">callbacks</span><span class="p">)),</span>
<span class="n">cast</span><span class="p">(</span><span class="n">c_array</span><span class="p">(</span><span class="n">CFUNCTYPE</span><span class="p">(</span><span class="n">c_int</span><span class="p">),</span> <span class="n">callbacks</span><span class="p">),</span>
<span class="n">POINTER</span><span class="p">(</span><span class="n">CFUNCTYPE</span><span class="p">(</span><span class="n">c_int</span><span class="p">))),</span>
<span class="n">cast</span><span class="p">(</span><span class="n">c_array</span><span class="p">(</span><span class="n">c_void_p</span><span class="p">,</span> <span class="p">[</span><span class="kc">None</span><span class="p">]</span><span class="o">*</span><span class="nb">len</span><span class="p">(</span><span class="n">callbacks</span><span class="p">)),</span>
<span class="n">POINTER</span><span class="p">(</span><span class="n">c_void_p</span><span class="p">)))</span>
<span class="n">check_call</span><span class="p">(</span><span class="n">_LIB</span><span class="o">.</span><span class="n">MXCustomFunctionRecord</span><span class="p">(</span>
<span class="n">c_int</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">inputs</span><span class="p">)),</span>
<span class="n">c_handle_array</span><span class="p">(</span><span class="n">inputs</span><span class="p">),</span>
<span class="n">c_int</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">outputs</span><span class="p">)),</span>
<span class="n">c_handle_array</span><span class="p">(</span><span class="n">outputs</span><span class="p">),</span>
<span class="n">ctypes</span><span class="o">.</span><span class="n">byref</span><span class="p">(</span><span class="n">context</span><span class="p">)))</span>
<span class="n">Function</span><span class="o">.</span><span class="n">_registry</span><span class="o">.</span><span class="n">ref_holder</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="n">context</span>
<span class="k">return</span> <span class="n">ret_outputs</span>
<div class="viewcode-block" id="Function.forward"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.Function.forward">[docs]</a> <span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">inputs</span><span class="p">):</span>
<span class="sd">"""Forward computation."""</span>
<span class="k">raise</span> <span class="ne">NotImplementedError</span></div>
<div class="viewcode-block" id="Function.backward"><a class="viewcode-back" href="../../api/python/autograd/autograd.html#mxnet.autograd.Function.backward">[docs]</a> <span class="k">def</span> <span class="nf">backward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">output_grads</span><span class="p">):</span>
<span class="sd">"""Backward computation.</span>
<span class="sd"> Takes as many inputs as forward's outputs,</span>
<span class="sd"> and returns as many NDArrays as forward's inputs.</span>
<span class="sd"> """</span>
<span class="k">raise</span> <span class="ne">NotImplementedError</span></div></div>
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