Creates a summary dict for tensor with associated symbol

        Args:
            voigt (bool): whether to get symbol dict for voigt
                notation tensor, as opposed to full notation,
                defaults to true
            zero_index (bool): whether to set initial index to zero,
                defaults to false, since tensor notations tend to use
                one-indexing, rather than zero indexing like python
            **kwargs: keyword args for np.isclose.  Can take atol
                and rtol for absolute and relative tolerance, e. g.

                >>> tensor.get_symbol_dict(atol=1e-8)

                or

                >>> tensor.get_symbol_dict(rtol=1e-5)

        Returns:
            list of index groups where tensor values are equivalent to
            within tolerances

        Returns:

def get_symbol_dict(self, voigt=True, zero_index=False, **kwargs):
        """
        Creates a summary dict for tensor with associated symbol

        Args:
            voigt (bool): whether to get symbol dict for voigt
                notation tensor, as opposed to full notation,
                defaults to true
            zero_index (bool): whether to set initial index to zero,
                defaults to false, since tensor notations tend to use
                one-indexing, rather than zero indexing like python
            **kwargs: keyword args for np.isclose.  Can take atol
                and rtol for absolute and relative tolerance, e. g.

                >>> tensor.get_symbol_dict(atol=1e-8)

                or

                >>> tensor.get_symbol_dict(rtol=1e-5)

        Returns:
            list of index groups where tensor values are equivalent to
            within tolerances

        Returns:

        """
        d = {}
        if voigt:
            array = self.voigt
        else:
            array = self
        grouped = self.get_grouped_indices(voigt=voigt, **kwargs)
        if zero_index:
            p = 0
        else:
            p = 1
        for indices in grouped:
            sym_string = self.symbol + '_'
            sym_string += ''.join([str(i + p) for i in indices[0]])
            value = array[indices[0]]
            if not np.isclose(value, 0):
                d[sym_string] = array[indices[0]]
        return d