a. If not found, repeat using directories in MATRIX_PATH=DIR1:DIR2:DIR3...</span>
<span class="kt">character</span><span class="p">(</span><span class="nb">len</span><span class="o">=*</span><span class="p">),</span><span class="k">intent</span><span class="p">(</span><span class="n">in</span><span class="p">)</span><span class="w">  </span><span class="kd">::</span><span class="w"> </span><span class="n">filename</span><span class="w"></span>
<span class="kt">character</span><span class="p">(</span><span c