def pretty_print(self, decimal_digits=2):
        """
        Returns a string repr of the wavefunction, ignoring all outcomes with approximately zero
        amplitude (up to a certain number of decimal digits) and rounding the amplitudes to
        decimal_digits.

        :param int decimal_digits: The number of digits to truncate to.
        :return: A dict with outcomes as keys and complex amplitudes as values.
        :rtype: str
        """
        outcome_dict = {}
        qubit_num = len(self)
        pp_string = ""
        for index, amplitude in enumerate(self.amplitudes):
            outcome = get_bitstring_from_index(index, qubit_num)
            amplitude = round(amplitude.real, decimal_digits) + \
                round(amplitude.imag, decimal_digits) * 1.j
            if amplitude != 0.:
                outcome_dict[outcome] = amplitude
                pp_string += str(amplitude) + "|{}> + ".format(outcome)
        if len(pp_string) >= 3:
            pp_string = pp_string[:-3]  # remove the dangling + if it is there
        return pp_string