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`); </script> <button class="sidebar-toggle secondary-toggle btn btn-sm" title="Toggle secondary sidebar" data-bs-placement="bottom" data-bs-toggle="tooltip"> <span class="fa-solid fa-list"></span> </button> </div></div> </div> </div> </div> <div id="jb-print-docs-body" class="onlyprint"> <h1>Flax</h1>  <div id="print-main-content"> <div id="jb-print-toc"> <div> <h2> Contents </h2> </div> <nav aria-label="Page"> <ul class="visible nav section-nav flex-column"> <li class="toc-h2 nav-item toc-entry"><a class="reference internal nav-link" href="#features">Features</a></li> <li class="toc-h2 nav-item toc-entry"><a class="reference internal nav-link" href="#basic-usage">Basic usage</a></li> <li class="toc-h2 nav-item toc-entry"><a class="reference internal nav-link" href="#installation">Installation</a></li> <li class="toc-h2 nav-item toc-entry"><a class="reference internal nav-link" href="#learn-more">Learn more</a></li> </ul> </nav> </div> </div> </div> <div id="searchbox"></div> <article class="bd-article"> <div class="section" id="flax"> <h1>Flax<a class="headerlink" href="#flax" title="Permalink to this heading">#</a></h1> <div class="sd-text-left sd-font-italic docutils"> <p><strong>N</strong>eural <strong>N</strong>etworks for JA<strong>X</strong></p> </div> <hr class="docutils" /> <p>Flax provides a <strong>flexible end-to-end user experience for researchers and developers who use JAX for neural networks</strong>. Flax enables you to use the full power of <a class="reference external" href="https://jax.readthedocs.io">JAX</a>.</p> <p>At the core of Flax is <strong>NNX - a simplified API that makes it easier to create, inspect, debug, and analyze neural networks in JAX.</strong> Flax NNX has first class support for Python reference semantics, enabling users to express their models using regular Python objects. Flax NNX is an evolution of the previous <a class="reference external" href="https://flax-linen.readthedocs.io/">Flax Linen</a> API, and it took years of experience to bring a simpler and more user-friendly API.</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>Flax Linen API is not going to be deprecated in the near future as most of Flax users still rely on this API. However, new users are encouraged to use Flax NNX. Check out <a class="reference external" href="why.html">Why Flax NNX</a> for a comparison between Flax NNX and Linen, and our reasoning to make the new API.</p> <p>To move your Flax Linen codebase to Flax NNX, get familiarized with the API in <a class="reference external" href="https://flax.readthedocs.io/en/latest/nnx_basics.html">NNX Basics</a> and then start your move following the <a class="reference external" href="guides/linen_to_nnx.html">evolution guide</a>.</p> </div> <div class="section" id="features"> <h2>Features<a class="headerlink" href="#features" title="Permalink to this heading">#</a></h2> <div class="sd-container-fluid sd-sphinx-override sd-mb-4 docutils"> <div class="sd-row docutils"> <div class="sd-col sd-d-flex-column sd-col-12 sd-col-xs-12 sd-col-sm-12 sd-col-md-12 sd-col-lg-6 docutils"> <div class="sd-card sd-sphinx-override sd-mb-3 sd-shadow-none sd-border-0 docutils"> <div class="sd-card-body docutils"> <div class="sd-card-title sd-font-weight-bold sd-fs-5 docutils"> Pythonic</div> <div class="sd-font-normal docutils"> <p class="sd-card-text">Flax NNX supports the use of regular Python objects, providing an intuitive and predictable development experience.</p> </div> </div> </div> </div> <div class="sd-col sd-d-flex-column sd-col-12 sd-col-xs-12 sd-col-sm-12 sd-col-md-12 sd-col-lg-6 docutils"> <div class="sd-card sd-sphinx-override sd-mb-3 sd-shadow-none sd-border-0 docutils"> <div class="sd-card-body docutils"> <div class="sd-card-title sd-font-weight-bold sd-fs-5 docutils"> Simple</div> <div class="sd-font-normal docutils"> <p class="sd-card-text">Flax NNX relies on Python鈥檚 object model, which results in simplicity for the user and increases development speed.</p> </div> </div> </div> </div> <div class="sd-col sd-d-flex-column sd-col-12 sd-col-xs-12 sd-col-sm-12 sd-col-md-12 sd-col-lg-6 docutils"> <div class="sd-card sd-sphinx-override sd-mb-3 sd-shadow-none sd-border-0 docutils"> <div class="sd-card-body docutils"> <div class="sd-card-title sd-font-weight-bold sd-fs-5 docutils"> Expressive</div> <div class="sd-font-normal docutils"> <p class="sd-card-text">Flax NNX allows fine-grained control of the model鈥檚 state via its <a class="reference external" href="https://flax.readthedocs.io/en/latest/nnx/filters_guide.html">Filter</a> system.</p> </div> </div> </div> </div> <div class="sd-col sd-d-flex-column sd-col-12 sd-col-xs-12 sd-col-sm-12 sd-col-md-12 sd-col-lg-6 docutils"> <div class="sd-card sd-sphinx-override sd-mb-3 sd-shadow-none sd-border-0 docutils"> <div class="sd-card-body docutils"> <div class="sd-card-title sd-font-weight-bold sd-fs-5 docutils"> Familiar</div> <div class="sd-font-normal docutils"> <p class="sd-card-text">Flax NNX makes it very easy to integrate objects with regular JAX code via the <a class="reference external" href="nnx_basics.html#the-flax-functional-api">Functional API</a>.</p> </div> </div> </div> </div> </div> </div> </div> <div class="section" id="basic-usage"> <h2>Basic usage<a class="headerlink" href="#basic-usage" title="Permalink to this heading">#</a></h2> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">flax</span> <span class="kn">import</span> <span class="n">nnx</span> <span class="kn">import</span> <span class="nn">optax</span> <span class="k">class</span> <span class="nc">Model</span><span class="p">(</span><span class="n">nnx</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span> <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">din</span><span class="p">,</span> <span class="n">dmid</span><span class="p">,</span> <span class="n">dout</span><span class="p">,</span> <span class="n">rngs</span><span class="p">:</span> <span class="n">nnx</span><span class="o">.</span><span class="n">Rngs</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">linear</span> <span class="o">=</span> <span class="n">nnx</span><span class="o">.</span><span class="n">Linear</span><span class="p">(</span><span class="n">din</span><span class="p">,</span> <span class="n">dmid</span><span class="p">,</span> <span class="n">rngs</span><span class="o">=</span><span class="n">rngs</span><span class="p">)</span> <span class="bp">self</span><span class="o">.</span><span class="n">bn</span> <span class="o">=</span> <span class="n">nnx</span><span class="o">.</span><span class="n">BatchNorm</span><span class="p">(</span><span class="n">dmid</span><span class="p">,</span> <span class="n">rngs</span><span class="o">=</span><span class="n">rngs</span><span class="p">)</span> <span class="bp">self</span><span class="o">.</span><span class="n">dropout</span> <span class="o">=</span> <span class="n">nnx</span><span class="o">.</span><span class="n">Dropout</span><span class="p">(</span><span class="mf">0.2</span><span class="p">,</span> <span class="n">rngs</span><span class="o">=</span><span class="n">rngs</span><span class="p">)</span> <span class="bp">self</span><span class="o">.</span><span class="n">linear_out</span> <span class="o">=</span> <span class="n">nnx</span><span class="o">.</span><span class="n">Linear</span><span class="p">(</span><span class="n">dmid</span><span class="p">,</span> <span class="n">dout</span><span class="p">,</span> <span class="n">rngs</span><span class="o">=</span><span class="n">rngs</span><span class="p">)</span> <span class="k">def</span> <span class="fm">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span> <span class="n">x</span> <span class="o">=</span> <span class="n">nnx</span><span class="o">.</span><span class="n">relu</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">dropout</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">bn</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">linear</span><span class="p">(</span><span class="n">x</span><span class="p">))))</span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">linear_out</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="n">model</span> <span class="o">=</span> <span class="n">Model</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="n">rngs</span><span class="o">=</span><span class="n">nnx</span><span class="o">.</span><span class="n">Rngs</span><span class="p">(</span><span class="mi">0</span><span class="p">))</span> <span class="c1"># eager initialization</span> <span class="n">optimizer</span> <span class="o">=</span> <span class="n">nnx</span><span class="o">.</span><span class="n">Optimizer</span><span class="p">(</span><span class="n">model</span><span class="p">,</span> <span class="n">optax</span><span class="o">.</span><span class="n">adam</span><span class="p">(</span><span class="mf">1e-3</span><span class="p">))</span> <span class="c1"># reference sharing</span> <span class="nd">@nnx</span><span class="o">.</span><span class="n">jit</span> <span class="c1"># automatic state management for JAX transforms</span> <span class="k">def</span> <span class="nf">train_step</span><span class="p">(</span><span class="n">model</span><span class="p">,</span> <span class="n">optimizer</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">):</span> <span class="k">def</span> <span class="nf">loss_fn</span><span class="p">(</span><span class="n">model</span><span class="p">):</span> <span class="n">y_pred</span> <span class="o">=</span> <span class="n">model</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="c1"># call methods directly</span> <span class="k">return</span> <span class="p">((</span><span class="n">y_pred</span> <span class="o">-</span> <span class="n">y</span><span class="p">)</span> <span class="o">**</span> <span class="mi">2</span><span class="p">)</span><span class="o">.</span><span class="n">mean</span><span class="p">()</span> <span class="n">loss</span><span class="p">,</span> <span class="n">grads</span> <span class="o">=</span> <span class="n">nnx</span><span class="o">.</span><span class="n">value_and_grad</span><span class="p">(</span><span class="n">loss_fn</span><span class="p">)(</span><span class="n">model</span><span class="p">)</span> <span class="n">optimizer</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="n">grads</span><span class="p">)</span> <span class="c1"># in-place updates</span> <span class="k">return</span> <span class="n">loss</span> </pre></div> </div> </div> <div class="section" id="installation"> <h2>Installation<a class="headerlink" href="#installation" title="Permalink to this heading">#</a></h2> <p>Install via pip:</p> <div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>pip<span class="w"> </span>install<span class="w"> </span>flax </pre></div> </div> <p>Or install the latest version from the repository:</p> <div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>pip<span class="w"> </span>install<span class="w"> </span>git+https://github.com/google/flax.git </pre></div> </div> </div> <hr class="docutils" /> <div class="section" id="learn-more"> <h2>Learn more<a class="headerlink" href="#learn-more" title="Permalink to this heading">#</a></h2> <div class="sd-container-fluid sd-sphinx-override sd-mb-4 docutils"> <div class="sd-row docutils"> <div 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C7.66,15,9,16.34,9,18z M13,9c0-1.1,0.9-2,2-2s2,0.9,2,2s-0.9,2-2,2S13,10.1,13,9z"></path></g></g></svg> Flax NNX Basics</div> </div> <a class="sd-stretched-link sd-hide-link-text reference external" href="nnx_basics.html"><span>nnx_basics.html</span></a></div> </div> <div class="sd-col sd-d-flex-column sd-col-6 sd-col-xs-6 sd-col-sm-6 sd-col-md-6 sd-col-lg-4 docutils"> <div class="sd-card sd-sphinx-override sd-mb-3 sd-shadow-sm sd-card-hover sd-text-black sd-bg-light docutils"> <div class="sd-card-body docutils"> <div class="sd-card-title sd-font-weight-bold docutils"> <svg version="4.0.0.63c5cb3" width="2.0em" height="2.0em" class="sd-material-icon sd-material-icon-library_books" viewBox="0 0 24 24" aria-hidden="true"><path d="M0 0h24v24H0z" fill="none"></path><path d="M4 6H2v14c0 1.1.9 2 2 2h14v-2H4V6zm16-4H8c-1.1 0-2 .9-2 2v12c0 1.1.9 2 2 2h12c1.1 0 2-.9 2-2V4c0-1.1-.9-2-2-2zm-1 9H9V9h10v2zm-4 4H9v-2h6v2zm4-8H9V5h10v2z"></path></svg> MNIST Tutorial</div> </div> <a 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d="M13,12.49v1.66c1.13-0.64,2.7-0.99,4.5-0.99c0.88,0,1.73,0.09,2.5,0.26V11.9c-0.79-0.15-1.64-0.24-2.5-0.24 C15.8,11.66,14.26,11.96,13,12.49z"></path><path d="M17.5,14.33c-1.7,0-3.24,0.29-4.5,0.83v1.66c1.13-0.64,2.7-0.99,4.5-0.99c0.88,0,1.73,0.09,2.5,0.26v-1.52 C19.21,14.41,18.36,14.33,17.5,14.33z"></path></g></g></g></svg> API reference</div> </div> <a class="sd-stretched-link sd-hide-link-text reference external" href="api_reference/index.html"><span>api_reference/index.html</span></a></div> </div> <div class="sd-col sd-d-flex-column sd-col-6 sd-col-xs-6 sd-col-sm-6 sd-col-md-6 sd-col-lg-4 docutils"> <div class="sd-card sd-sphinx-override sd-mb-3 sd-shadow-sm sd-card-hover sd-text-black sd-bg-light docutils"> <div class="sd-card-body docutils"> <div class="sd-card-title sd-font-weight-bold docutils"> <svg version="4.0.0.63c5cb3" width="2.0em" height="2.0em" class="sd-material-icon sd-material-icon-import_contacts" viewBox="0 0 24 24" aria-hidden="true"><g><rect fill="none" height="24" 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