at position (i,j) indicates if the point is a dummy point,</span>
<span class="sd">        whereas ``0`` indicates a dummy point used for padding; (3)</span>
<span class="sd">        the max. number of points and (4) the batch size.</span>

<span class="sd">    Example::</span>

<span class="sd">        &gt;&gt;&gt; from torchph.nn.slayer import prepare_batch</span>
<span class="sd">        &gt;&gt;&gt; import torch</span>
<span class="sd">        &gt;&gt;&gt; x = [torch.rand(10,2), torch.rand(20,2)]</span>