Tools /
## MpReorderSymmetryThe ## Synopsis
## Options
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`--force` overwrite the output file, if it exists
## DescriptionThe If the output file already exists, then ## Examples- Reorder the symmetry labels of a wavefunction.
If`psi1` has a symmetry list of`Sz:U(1),N:U(1)` , but you want to use operators defined on a Hubbard model lattice that has a symmetry list of`N:U(1),Sz:U(1)` , then use`mp-reorder-symmetry "N:U(1),Sz:U(1)" psi1 psi2` If`psi2` already exists, then this will fail with an error, leaving the existing file`psi2` untouched. To force overwriting`psi2` , add the`-f` option.
- Remove the symmetries from a wavefunction
`mp-reorder-symmetry "Null:Null" psi1 psi2`
- Remove the symmetries from an {$SU(2)$} spin chain. This is a 2-step process as we first need to project the {$SU(2)$} symmetry down to {$U(1)$}.
mp-wigner-eckart "Sz:U(1)" psi1 psi2 mp-reorder-symmetry "Null:Null" psi2
## Notes- The symmetry list of wavefunctions must
*exactly*match the symmetry list of the lattice file, so it is sometimes necessary to reorder the symmetry list as a result of some wavefunction transformation. For example, it might be necessary to reorder`Sz:U(1),N:U(1)` into`N:U(1),Sz:U(1)` in order to reuse an existing Hubbard model lattice file.
- Another use for
`mp-reorder-symmetry` is for removing quantum numbers in order to apply a transformation or calculate an expectation value that isn't compatible with the original symmetries. For example, given an {$U(1)$} invariant spin chain, to calculate the dihedral group projective symmetry relations for {$\pi$} rotations about the x,y,z axes the symmetry must be removed, because operators such as {$\exp[ i \pi S^x]$} do not commute with {$S^z$}. Quantum numbers can only be removed if the representation has degree 1 (ie, they are abelian, or in the abelian subset of a non-abelian symmetry).
- New quantum numbers can be added to the symmetry list, and they are set to the scalar quantum number.
- The symmetry-list is not allowed to be empty, so if removing all symmetries, use a symmetry-list of
`Null:Null` .
## See also |

Page last modified on May 11, 2017, at 05:10 PM