<p>In <a href="https://github.com/mlpack/mlpack/pull/703#discussion_r74704105">src/mlpack/methods/edge_boxes/feature_extraction_impl.hpp</a>:</p>
<pre style='color:#555'>&gt; +void StructuredForests&lt;MatType, CubeType&gt;::
&gt; +DistanceTransform1D(const arma::vec&amp; f, const size_t n, const double inf,
&gt; +                    arma::vec&amp; d)
&gt; +{
&gt; +  arma::vec v(n), z(n + 1);
&gt; +  d = arma::vec(n);
&gt; +  size_t k = 0;
&gt; +  v[0] = 0.0;
&gt; +  z[0] = -inf;
&gt; +  z[1] = inf;
&gt; +  for (size_t q = 1; q &lt;= n - 1; ++q)
&gt; +  {
&gt; +    float s  = ( (f[q] + q * q)-( f[v[k]] + v[k] * v[k]) ) / (2 * q - 2 * v[k]);
&gt; +    while (s &lt;= z[k])
&gt; +    {
&gt; +      --k;
</pre>
<p>I'm not sure, but if we set k = 0 at the beginning, how can we decrease k (<code>size_t</code>), and still get the right index?</p>

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