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<div class="section" id="customized-loss-function">
<span id="customized-loss-function"></span><h1>Customized loss function<a class="headerlink" href="#customized-loss-function" title="Permalink to this headline">¶</a></h1>
<p>This tutorial provides guidelines for using customized loss function in network construction.</p>
<div class="section" id="model-training-example">
<span id="model-training-example"></span><h2>Model Training Example<a class="headerlink" href="#model-training-example" title="Permalink to this headline">¶</a></h2>
<p>Let’s begin with a small regression example. We can build and train a regression model with the following code:</p>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="nf">data</span><span class="p">(</span><span class="n">BostonHousing</span><span class="p">,</span> <span class="n">package</span> <span class="o">=</span> <span class="s">"mlbench"</span><span class="p">)</span>
<span class="n">BostonHousing[</span><span class="p">,</span> <span class="nf">sapply</span><span class="p">(</span><span class="n">BostonHousing</span><span class="p">,</span> <span class="n">is.factor</span><span class="p">)</span><span class="n">]</span> <span class="o"><-</span>
<span class="nf">as.numeric</span><span class="p">(</span><span class="nf">as.character</span><span class="p">(</span><span class="n">BostonHousing[</span><span class="p">,</span> <span class="nf">sapply</span><span class="p">(</span><span class="n">BostonHousing</span><span class="p">,</span> <span class="n">is.factor</span><span class="p">)</span><span class="n">]</span><span class="p">))</span>
<span class="n">BostonHousing</span> <span class="o"><-</span> <span class="nf">data.frame</span><span class="p">(</span><span class="nf">scale</span><span class="p">(</span><span class="n">BostonHousing</span><span class="p">))</span>
<span class="n">test.ind</span> <span class="o">=</span> <span class="nf">seq</span><span class="p">(</span><span class="m">1</span><span class="p">,</span> <span class="m">506</span><span class="p">,</span> <span class="m">5</span><span class="p">)</span> <span class="c1"># 1 pt in 5 used for testing</span>
<span class="n">train.x</span> <span class="o">=</span> <span class="nf">data.matrix</span><span class="p">(</span><span class="n">BostonHousing[</span><span class="o">-</span><span class="n">test.ind</span><span class="p">,</span><span class="m">-14</span><span class="n">]</span><span class="p">)</span>
<span class="n">train.y</span> <span class="o">=</span> <span class="n">BostonHousing[</span><span class="o">-</span><span class="n">test.ind</span><span class="p">,</span> <span class="m">14</span><span class="n">]</span>
<span class="n">test.x</span> <span class="o">=</span> <span class="nf">data.matrix</span><span class="p">(</span><span class="n">BostonHousing[</span><span class="o">--</span><span class="n">test.ind</span><span class="p">,</span><span class="m">-14</span><span class="n">]</span><span class="p">)</span>
<span class="n">test.y</span> <span class="o">=</span> <span class="n">BostonHousing[</span><span class="o">--</span><span class="n">test.ind</span><span class="p">,</span> <span class="m">14</span><span class="n">]</span>
<span class="nf">require</span><span class="p">(</span><span class="n">mxnet</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Loading required package: mxnet</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">data</span> <span class="o"><-</span> <span class="nf">mx.symbol.Variable</span><span class="p">(</span><span class="s">"data"</span><span class="p">)</span>
<span class="n">label</span> <span class="o"><-</span> <span class="nf">mx.symbol.Variable</span><span class="p">(</span><span class="s">"label"</span><span class="p">)</span>
<span class="n">fc1</span> <span class="o"><-</span> <span class="nf">mx.symbol.FullyConnected</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">num_hidden</span> <span class="o">=</span> <span class="m">14</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"fc1"</span><span class="p">)</span>
<span class="n">tanh1</span> <span class="o"><-</span> <span class="nf">mx.symbol.Activation</span><span class="p">(</span><span class="n">fc1</span><span class="p">,</span> <span class="n">act_type</span> <span class="o">=</span> <span class="s">"tanh"</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"tanh1"</span><span class="p">)</span>
<span class="n">fc2</span> <span class="o"><-</span> <span class="nf">mx.symbol.FullyConnected</span><span class="p">(</span><span class="n">tanh1</span><span class="p">,</span> <span class="n">num_hidden</span> <span class="o">=</span> <span class="m">1</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"fc2"</span><span class="p">)</span>
<span class="n">lro</span> <span class="o"><-</span> <span class="nf">mx.symbol.LinearRegressionOutput</span><span class="p">(</span><span class="n">fc2</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"lro"</span><span class="p">)</span>
<span class="nf">mx.set.seed</span><span class="p">(</span><span class="m">0</span><span class="p">)</span>
<span class="n">model</span> <span class="o"><-</span> <span class="nf">mx.model.FeedForward.create</span><span class="p">(</span><span class="n">lro</span><span class="p">,</span> <span class="n">X</span> <span class="o">=</span> <span class="n">train.x</span><span class="p">,</span> <span class="n">y</span> <span class="o">=</span> <span class="n">train.y</span><span class="p">,</span>
<span class="n">ctx</span> <span class="o">=</span> <span class="nf">mx.cpu</span><span class="p">(),</span>
<span class="n">num.round</span> <span class="o">=</span> <span class="m">5</span><span class="p">,</span>
<span class="n">array.batch.size</span> <span class="o">=</span> <span class="m">60</span><span class="p">,</span>
<span class="n">optimizer</span> <span class="o">=</span> <span class="s">"rmsprop"</span><span class="p">,</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="kc">TRUE</span><span class="p">,</span>
<span class="n">array.layout</span> <span class="o">=</span> <span class="s">"rowmajor"</span><span class="p">,</span>
<span class="n">batch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">,</span>
<span class="n">epoch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Start training with 1 devices</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">pred</span> <span class="o"><-</span> <span class="nf">predict</span><span class="p">(</span><span class="n">model</span><span class="p">,</span> <span class="n">test.x</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Warning in mx.model.select.layout.predict(X, model): Auto detect layout of input matrix, use rowmajor..</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="nf">sum</span><span class="p">((</span><span class="n">test.y</span> <span class="o">-</span> <span class="n">pred[1</span><span class="p">,</span><span class="n">]</span><span class="p">)</span><span class="n">^2</span><span class="p">)</span> <span class="o">/</span> <span class="nf">length</span><span class="p">(</span><span class="n">test.y</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## [1] 0.2485236</span>
</pre></div>
</div>
<p>Besides the <code class="docutils literal"><span class="pre">LinearRegressionOutput</span></code>, we also provide <code class="docutils literal"><span class="pre">LogisticRegressionOutput</span></code> and <code class="docutils literal"><span class="pre">MAERegressionOutput</span></code>. However, this might not be enough for real-world models. You can provide your own loss function by using <code class="docutils literal"><span class="pre">mx.symbol.MakeLoss</span></code> when constructing the network.</p>
</div>
<div class="section" id="how-to-use-your-own-loss-function">
<span id="how-to-use-your-own-loss-function"></span><h2>How to Use Your Own Loss Function<a class="headerlink" href="#how-to-use-your-own-loss-function" title="Permalink to this headline">¶</a></h2>
<p>We still use our previous example, but this time we use <code class="docutils literal"><span class="pre">mx.symbol.MakeLoss</span></code> to minimize the <code class="docutils literal"><span class="pre">(pred-label)^2</span></code></p>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">data</span> <span class="o"><-</span> <span class="nf">mx.symbol.Variable</span><span class="p">(</span><span class="s">"data"</span><span class="p">)</span>
<span class="n">label</span> <span class="o"><-</span> <span class="nf">mx.symbol.Variable</span><span class="p">(</span><span class="s">"label"</span><span class="p">)</span>
<span class="n">fc1</span> <span class="o"><-</span> <span class="nf">mx.symbol.FullyConnected</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">num_hidden</span> <span class="o">=</span> <span class="m">14</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"fc1"</span><span class="p">)</span>
<span class="n">tanh1</span> <span class="o"><-</span> <span class="nf">mx.symbol.Activation</span><span class="p">(</span><span class="n">fc1</span><span class="p">,</span> <span class="n">act_type</span> <span class="o">=</span> <span class="s">"tanh"</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"tanh1"</span><span class="p">)</span>
<span class="n">fc2</span> <span class="o"><-</span> <span class="nf">mx.symbol.FullyConnected</span><span class="p">(</span><span class="n">tanh1</span><span class="p">,</span> <span class="n">num_hidden</span> <span class="o">=</span> <span class="m">1</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"fc2"</span><span class="p">)</span>
<span class="n">lro2</span> <span class="o"><-</span> <span class="nf">mx.symbol.MakeLoss</span><span class="p">(</span><span class="nf">mx.symbol.square</span><span class="p">(</span><span class="nf">mx.symbol.Reshape</span><span class="p">(</span><span class="n">fc2</span><span class="p">,</span> <span class="n">shape</span> <span class="o">=</span> <span class="m">0</span><span class="p">)</span> <span class="o">-</span> <span class="n">label</span><span class="p">),</span> <span class="n">name</span><span class="o">=</span><span class="s">"lro2"</span><span class="p">)</span>
</pre></div>
</div>
<p>Then we can train the network just as usual.</p>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="nf">mx.set.seed</span><span class="p">(</span><span class="m">0</span><span class="p">)</span>
<span class="n">model2</span> <span class="o"><-</span> <span class="nf">mx.model.FeedForward.create</span><span class="p">(</span><span class="n">lro2</span><span class="p">,</span> <span class="n">X</span> <span class="o">=</span> <span class="n">train.x</span><span class="p">,</span> <span class="n">y</span> <span class="o">=</span> <span class="n">train.y</span><span class="p">,</span>
<span class="n">ctx</span> <span class="o">=</span> <span class="nf">mx.cpu</span><span class="p">(),</span>
<span class="n">num.round</span> <span class="o">=</span> <span class="m">5</span><span class="p">,</span>
<span class="n">array.batch.size</span> <span class="o">=</span> <span class="m">60</span><span class="p">,</span>
<span class="n">optimizer</span> <span class="o">=</span> <span class="s">"rmsprop"</span><span class="p">,</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="kc">TRUE</span><span class="p">,</span>
<span class="n">array.layout</span> <span class="o">=</span> <span class="s">"rowmajor"</span><span class="p">,</span>
<span class="n">batch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">,</span>
<span class="n">epoch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Start training with 1 devices</span>
</pre></div>
</div>
<p>We should get very similar results because we are actually minimizing the same loss function. However, the result is quite different.</p>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">pred2</span> <span class="o"><-</span> <span class="nf">predict</span><span class="p">(</span><span class="n">model2</span><span class="p">,</span> <span class="n">test.x</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Warning in mx.model.select.layout.predict(X, model): Auto detect layout of input matrix, use rowmajor..</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="nf">sum</span><span class="p">((</span><span class="n">test.y</span> <span class="o">-</span> <span class="n">pred2</span><span class="p">)</span><span class="n">^2</span><span class="p">)</span> <span class="o">/</span> <span class="nf">length</span><span class="p">(</span><span class="n">test.y</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## [1] 1.234584</span>
</pre></div>
</div>
<p>This is because output of <code class="docutils literal"><span class="pre">mx.symbol.MakeLoss</span></code> is the gradient of loss with respect to the input data. We can get the real prediction as below.</p>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">internals</span> <span class="o">=</span> <span class="nf">internals</span><span class="p">(</span><span class="n">model2</span><span class="o">$</span><span class="n">symbol</span><span class="p">)</span>
<span class="n">fc_symbol</span> <span class="o">=</span> <span class="n">internals[</span><span class="nf">[match</span><span class="p">(</span><span class="s">"fc2_output"</span><span class="p">,</span> <span class="nf">outputs</span><span class="p">(</span><span class="n">internals</span><span class="p">))</span><span class="n">]]</span>
<span class="n">model3</span> <span class="o"><-</span> <span class="nf">list</span><span class="p">(</span><span class="n">symbol</span> <span class="o">=</span> <span class="n">fc_symbol</span><span class="p">,</span>
<span class="n">arg.params</span> <span class="o">=</span> <span class="n">model2</span><span class="o">$</span><span class="n">arg.params</span><span class="p">,</span>
<span class="n">aux.params</span> <span class="o">=</span> <span class="n">model2</span><span class="o">$</span><span class="n">aux.params</span><span class="p">)</span>
<span class="nf">class</span><span class="p">(</span><span class="n">model3</span><span class="p">)</span> <span class="o"><-</span> <span class="s">"MXFeedForwardModel"</span>
<span class="n">pred3</span> <span class="o"><-</span> <span class="nf">predict</span><span class="p">(</span><span class="n">model3</span><span class="p">,</span> <span class="n">test.x</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Warning in mx.model.select.layout.predict(X, model): Auto detect layout of input matrix, use rowmajor..</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="nf">sum</span><span class="p">((</span><span class="n">test.y</span> <span class="o">-</span> <span class="n">pred3[1</span><span class="p">,</span><span class="n">]</span><span class="p">)</span><span class="n">^2</span><span class="p">)</span> <span class="o">/</span> <span class="nf">length</span><span class="p">(</span><span class="n">test.y</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## [1] 0.248294</span>
</pre></div>
</div>
<p>We have provided many operations on the symbols. An example of <code class="docutils literal"><span class="pre">|pred-label|</span></code> can be found below.</p>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">lro_abs</span> <span class="o"><-</span> <span class="nf">mx.symbol.MakeLoss</span><span class="p">(</span><span class="nf">mx.symbol.abs</span><span class="p">(</span><span class="nf">mx.symbol.Reshape</span><span class="p">(</span><span class="n">fc2</span><span class="p">,</span> <span class="n">shape</span> <span class="o">=</span> <span class="m">0</span><span class="p">)</span> <span class="o">-</span> <span class="n">label</span><span class="p">))</span>
<span class="nf">mx.set.seed</span><span class="p">(</span><span class="m">0</span><span class="p">)</span>
<span class="n">model4</span> <span class="o"><-</span> <span class="nf">mx.model.FeedForward.create</span><span class="p">(</span><span class="n">lro_abs</span><span class="p">,</span> <span class="n">X</span> <span class="o">=</span> <span class="n">train.x</span><span class="p">,</span> <span class="n">y</span> <span class="o">=</span> <span class="n">train.y</span><span class="p">,</span>
<span class="n">ctx</span> <span class="o">=</span> <span class="nf">mx.cpu</span><span class="p">(),</span>
<span class="n">num.round</span> <span class="o">=</span> <span class="m">20</span><span class="p">,</span>
<span class="n">array.batch.size</span> <span class="o">=</span> <span class="m">60</span><span class="p">,</span>
<span class="n">optimizer</span> <span class="o">=</span> <span class="s">"sgd"</span><span class="p">,</span>
<span class="n">learning.rate</span> <span class="o">=</span> <span class="m">0.001</span><span class="p">,</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="kc">TRUE</span><span class="p">,</span>
<span class="n">array.layout</span> <span class="o">=</span> <span class="s">"rowmajor"</span><span class="p">,</span>
<span class="n">batch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">,</span>
<span class="n">epoch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Start training with 1 devices</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">internals</span> <span class="o">=</span> <span class="nf">internals</span><span class="p">(</span><span class="n">model4</span><span class="o">$</span><span class="n">symbol</span><span class="p">)</span>
<span class="n">fc_symbol</span> <span class="o">=</span> <span class="n">internals[</span><span class="nf">[match</span><span class="p">(</span><span class="s">"fc2_output"</span><span class="p">,</span> <span class="nf">outputs</span><span class="p">(</span><span class="n">internals</span><span class="p">))</span><span class="n">]]</span>
<span class="n">model5</span> <span class="o"><-</span> <span class="nf">list</span><span class="p">(</span><span class="n">symbol</span> <span class="o">=</span> <span class="n">fc_symbol</span><span class="p">,</span>
<span class="n">arg.params</span> <span class="o">=</span> <span class="n">model4</span><span class="o">$</span><span class="n">arg.params</span><span class="p">,</span>
<span class="n">aux.params</span> <span class="o">=</span> <span class="n">model4</span><span class="o">$</span><span class="n">aux.params</span><span class="p">)</span>
<span class="nf">class</span><span class="p">(</span><span class="n">model5</span><span class="p">)</span> <span class="o"><-</span> <span class="s">"MXFeedForwardModel"</span>
<span class="n">pred5</span> <span class="o"><-</span> <span class="nf">predict</span><span class="p">(</span><span class="n">model5</span><span class="p">,</span> <span class="n">test.x</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Warning in mx.model.select.layout.predict(X, model): Auto detect layout of input matrix, use rowmajor..</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="nf">sum</span><span class="p">(</span><span class="nf">abs</span><span class="p">(</span><span class="n">test.y</span> <span class="o">-</span> <span class="n">pred5[1</span><span class="p">,</span><span class="n">]</span><span class="p">))</span> <span class="o">/</span> <span class="nf">length</span><span class="p">(</span><span class="n">test.y</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## [1] 0.7056902</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">lro_mae</span> <span class="o"><-</span> <span class="nf">mx.symbol.MAERegressionOutput</span><span class="p">(</span><span class="n">fc2</span><span class="p">,</span> <span class="n">name</span> <span class="o">=</span> <span class="s">"lro"</span><span class="p">)</span>
<span class="nf">mx.set.seed</span><span class="p">(</span><span class="m">0</span><span class="p">)</span>
<span class="n">model6</span> <span class="o"><-</span> <span class="nf">mx.model.FeedForward.create</span><span class="p">(</span><span class="n">lro_mae</span><span class="p">,</span> <span class="n">X</span> <span class="o">=</span> <span class="n">train.x</span><span class="p">,</span> <span class="n">y</span> <span class="o">=</span> <span class="n">train.y</span><span class="p">,</span>
<span class="n">ctx</span> <span class="o">=</span> <span class="nf">mx.cpu</span><span class="p">(),</span>
<span class="n">num.round</span> <span class="o">=</span> <span class="m">20</span><span class="p">,</span>
<span class="n">array.batch.size</span> <span class="o">=</span> <span class="m">60</span><span class="p">,</span>
<span class="n">optimizer</span> <span class="o">=</span> <span class="s">"sgd"</span><span class="p">,</span>
<span class="n">learning.rate</span> <span class="o">=</span> <span class="m">0.001</span><span class="p">,</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="kc">TRUE</span><span class="p">,</span>
<span class="n">array.layout</span> <span class="o">=</span> <span class="s">"rowmajor"</span><span class="p">,</span>
<span class="n">batch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">,</span>
<span class="n">epoch.end.callback</span> <span class="o">=</span> <span class="kc">NULL</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Start training with 1 devices</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="n">pred6</span> <span class="o"><-</span> <span class="nf">predict</span><span class="p">(</span><span class="n">model6</span><span class="p">,</span> <span class="n">test.x</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## Warning in mx.model.select.layout.predict(X, model): Auto detect layout of input matrix, use rowmajor..</span>
</pre></div>
</div>
<div class="highlight-r"><div class="highlight"><pre><span></span><span class="nf">sum</span><span class="p">(</span><span class="nf">abs</span><span class="p">(</span><span class="n">test.y</span> <span class="o">-</span> <span class="n">pred6[1</span><span class="p">,</span><span class="n">]</span><span class="p">))</span> <span class="o">/</span> <span class="nf">length</span><span class="p">(</span><span class="n">test.y</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">## [1] 0.7056902</span>
</pre></div>
</div>
</div>
<div class="section" id="next-steps">
<span id="next-steps"></span><h2>Next Steps<a class="headerlink" href="#next-steps" title="Permalink to this headline">¶</a></h2>
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<li class="toctree-l1"><a class="reference external" href="/versions/0.11.0/tutorials/r/classifyRealImageWithPretrainedModel.html">Classify Real-World Images with a PreTrained Model</a></li>
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<li><a class="reference internal" href="#">Customized loss function</a><ul>
<li><a class="reference internal" href="#model-training-example">Model Training Example</a></li>
<li><a class="reference internal" href="#how-to-use-your-own-loss-function">How to Use Your Own Loss Function</a></li>
<li><a class="reference internal" href="#next-steps">Next Steps</a></li>
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