code: public int[] getJC()
      {
          int[] jc = new int[getN()+1];
          // jc[j] is the number of nonzero elements in all preceeding columns
          for ( IndexMN index : indexSet )
          {
              for (int column = index.n + 1; column < jc.length; column++)
              {
                  jc[column]++;
              }
          }
          return jc;
      }
docs: Gets column indices.
  
  <tt>jc</tt> points to an integer array of length N+1 that contains column index information.
  For j, in the range <tt>0&lt;=j&lt;=N</tt>, <tt>jc[j]</tt> is the index in ir and <tt>pr</tt> (and <tt>pi</tt>
  if it exists) of the first nonzero entry in the jth column and <tt>jc[j+1]�1</tt> index
  of the last nonzero entry. As a result, <tt>jc[N]</tt> is also equal to nnz, the number
  of nonzero entries in the matrix. If nnz is less than nzmax, then more nonzero
  entries can be inserted in the array without allocating additional storage
  
  @return