code: private int getIndex(int row, int column) {
          int i = no.uib.cipr.matrix.sparse.Arrays.binarySearch(rowIndex, row,
                  columnPointer[column], columnPointer[column + 1]);
  
          if (i >= 0 && rowIndex[i] == row)
              return i;
          else
              throw new IndexOutOfBoundsException("Entry (" + (row + 1) + ", "
                      + (column + 1) + ") is not in the matrix structure");
      }
docs: Finds the insertion index