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