9;s Orthogonal Matching Pursuit. The gradients computed are on the </span>
<span class="sd">    hypothesized labels of the loss function and are matched to either the full gradient of these hypothesized </span>
<span class="sd">    examples or a supplied validation gradient. The indices returned are the ones selected by this algorithm.</span>
<span class="sd">    </span>
<span class="sd">    .. math::</span>
<span class="sd">        Err(X_t, L, L_T, \\theta_t) = \\left |\\left| \\sum_{i \\in X_t} \\nabla_\\