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<!DOCTYPE html> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>super_gradients.training.losses.focal_loss — SuperGradients 3.0.3 documentation</title> <link rel="stylesheet" href="../../../../_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="../../../../_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="../../../../_static/graphviz.css" type="text/css" /> <link rel="stylesheet" href="../../../../_static/custom.css" type="text/css" /> <!--[if lt IE 9]> <script src="../../../../_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="../../../../" id="documentation_options" src="../../../../_static/documentation_options.js"></script> <script src="../../../../_static/jquery.js"></script> <script src="../../../../_static/underscore.js"></script> <script src="../../../../_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="../../../../_static/doctools.js"></script> <script src="../../../../_static/sphinx_highlight.js"></script> <script src="../../../../_static/js/theme.js"></script> <link rel="index" title="Index" href="../../../../genindex.html" /> <link rel="search" title="Search" href="../../../../search.html" /> </head> <body class="wy-body-for-nav"> <div class="wy-grid-for-nav"> <nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="../../../../index.html" class="icon icon-home"> SuperGradients </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="../../../../search.html" method="get"> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> </div><div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="Navigation menu"> <p class="caption" role="heading"><span class="caption-text">Welcome To SuperGradients</span></p> <ul> <li class="toctree-l1"><a class="reference internal" href="../../../../welcome.html">Version 3 is out! 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itemscope="itemscope" itemtype="http://schema.org/Article"> <div itemprop="articleBody"> <h1>Source code for super_gradients.training.losses.focal_loss</h1><div class="highlight"><pre> <span></span><span class="kn">import</span> <span class="nn">torch</span> <span class="kn">from</span> <span class="nn">torch</span> <span class="kn">import</span> <span class="n">nn</span> <span class="kn">from</span> <span class="nn">torch.nn.modules.loss</span> <span class="kn">import</span> <span class="n">_Loss</span> <div class="viewcode-block" id="FocalLoss"><a class="viewcode-back" href="../../../../super_gradients.training.html#super_gradients.training.losses.FocalLoss">[docs]</a><span class="k">class</span> <span class="nc">FocalLoss</span><span class="p">(</span><span class="n">_Loss</span><span class="p">):</span> <span class="sd">"""Wraps focal loss around existing loss_fcn(), i.e. criteria = FocalLoss(nn.BCEWithLogitsLoss(), gamma=1.5)"""</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">loss_fcn</span><span class="p">:</span> <span class="n">nn</span><span class="o">.</span><span class="n">BCEWithLogitsLoss</span><span class="p">,</span> <span class="n">gamma</span><span class="o">=</span><span class="mf">1.5</span><span class="p">,</span> <span class="n">alpha</span><span class="o">=</span><span class="mf">0.25</span><span class="p">):</span> <span class="nb">super</span><span class="p">(</span><span class="n">FocalLoss</span><span class="p">,</span> <span class="bp">self</span><span class="p">)</span><span class="o">.</span><span class="fm">__init__</span><span class="p">()</span> <span class="bp">self</span><span class="o">.</span><span class="n">loss_fcn</span> <span class="o">=</span> <span class="n">loss_fcn</span> <span class="c1"># must be nn.BCEWithLogitsLoss()</span> <span class="bp">self</span><span class="o">.</span><span class="n">gamma</span> <span class="o">=</span> <span class="n">gamma</span> <span class="bp">self</span><span class="o">.</span><span class="n">alpha</span> <span class="o">=</span> <span class="n">alpha</span> <span class="bp">self</span><span class="o">.</span><span class="n">reduction</span> <span class="o">=</span> <span class="n">loss_fcn</span><span class="o">.</span><span class="n">reduction</span> <span class="bp">self</span><span class="o">.</span><span class="n">loss_fcn</span><span class="o">.</span><span class="n">reduction</span> <span class="o">=</span> <span class="s1">'none'</span> <span class="c1"># required to apply FocalLoss to each element</span> <div class="viewcode-block" id="FocalLoss.forward"><a class="viewcode-back" href="../../../../super_gradients.training.html#super_gradients.training.losses.FocalLoss.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="n">pred</span><span class="p">,</span> <span class="n">true</span><span class="p">):</span> <span class="n">loss</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">loss_fcn</span><span class="p">(</span><span class="n">pred</span><span class="p">,</span> <span class="n">true</span><span class="p">)</span> <span class="n">pred_prob</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">sigmoid</span><span class="p">(</span><span class="n">pred</span><span class="p">)</span> <span class="c1"># prob from logits</span> <span class="n">p_t</span> <span class="o">=</span> <span class="n">true</span> <span class="o">*</span> <span class="n">pred_prob</span> <span class="o">+</span> <span class="p">(</span><span class="mi">1</span> <span class="o">-</span> <span class="n">true</span><span class="p">)</span> <span class="o">*</span> <span class="p">(</span><span class="mi">1</span> <span class="o">-</span> <span class="n">pred_prob</span><span class="p">)</span> <span class="n">alpha_factor</span> <span class="o">=</span> <span class="n">true</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">alpha</span> <span class="o">+</span> <span class="p">(</span><span class="mi">1</span> <span class="o">-</span> <span class="n">true</span><span class="p">)</span> <span class="o">*</span> <span class="p">(</span><span class="mi">1</span> <span class="o">-</span> <span class="bp">self</span><span class="o">.</span><span class="n">alpha</span><span class="p">)</span> <span class="n">modulating_factor</span> <span class="o">=</span> <span class="p">(</span><span class="mf">1.0</span> <span class="o">-</span> <span class="n">p_t</span><span class="p">)</span> <span class="o">**</span> <span class="bp">self</span><span class="o">.</span><span class="n">gamma</span> <span class="n">loss</span> <span class="o">*=</span> <span class="n">alpha_factor</span> <span class="o">*</span> <span class="n">modulating_factor</span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">reduction</span> <span class="o">==</span> <span class="s1">'mean'</span><span class="p">:</span> <span class="k">return</span> <span class="n">loss</span><span class="o">.</span><span class="n">mean</span><span class="p">()</span> <span class="k">elif</span> <span class="bp">self</span><span class="o">.</span><span class="n">reduction</span> <span class="o">==</span> <span class="s1">'sum'</span><span class="p">:</span> <span class="k">return</span> <span class="n">loss</span><span class="o">.</span><span class="n">sum</span><span class="p">()</span> <span class="k">else</span><span class="p">:</span> <span class="c1"># 'none'</span> <span class="k">return</span> <span class="n">loss</span></div></div> </pre></div> </div> </div> <footer> <hr/> <div role="contentinfo"> <p>© Copyright 2021, 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