'update the element at matrix[row,col] to val.
:type row: int
:type col: int
:type val: int
:rtype: void'

def update(self, row, col, val):

    if (val - self.__matrix[row][col]):
        self.__add(row, col, (val - self.__matrix[row][col]))
        self.__matrix[row][col] = val
