/span><span class="k">class</span> <span class="nc">SparseTriangularMatrix</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="bp">self</span><span class="o">.</span><span class="n">matrix</span> <span class="o">=</span> <span class="p">{}</span>  

    <span class="k">def</span> <span class="fm">__str__</span><span class="p">(</span><span class="bp">self</span><span c