Path types and rejection reasons¶

During a PyRETIS simulation, each Monte Carlo cycle generates (or loads) a path and records two short codes in the output:

Both codes appear in the per-ensemble output files and in the simulation log, e.g.:

# Cycle: 42, status: ACC, move: sh

The tables below list every code that PyRETIS can produce.

Move types¶

The move type describes how the new path was generated.

Code	Short name	Description
`sh`	Shoot	Path generated with a shooting move: a phase-space point is selected on the current path, momenta are perturbed, and new forward and backward trajectories are integrated.
`ss`	Stone skipping	Path generated by the Stone Skipping algorithm, a multi-step variant of shooting that reuses short sub-paths.
`wt`	Web Throwing	Path generated by the Web Throwing move.
`wf`	Wire Fencing	Path generated by the Wire Fencing move.
`ts`	Target swap	Path generated by a target swap move.
`tr`	Time-reversal	Path generated by time-reversal: the current accepted path is reversed in time to produce the trial path.
`s+`	Swap from +	Path produced by a replica-swap move where the incoming path came from the `+` (higher-index) ensemble.
`s-`	Swap from −	Path produced by a replica-swap move where the incoming path came from the `-` (lower-index) ensemble.
`mr`	Mirror	Path generated by a mirror move.
`ki`	Kick initiation	Path generated by integrating the equations of motion after kicking (re-drawing) the initial momenta; used during path initiation.
`is`	Initial shoot	Path generated by a shooting move applied during the initial Stone Skipping preparation step, before the actual SS move.
`ld`	Load (unformatted)	Path loaded from unformatted (binary) external file(s).
`re`	Load (formatted)	Path loaded from formatted (text) external file(s).
`00`	Null move	Path produced by a null move: the current path is kept without any modification (used internally).

The status code explains why the trial path was accepted or, if rejected, what condition was violated.

Acceptance

Code	Meaning
`ACC`	The trial path was accepted and becomes the new current path.

Trajectory-length rejections

These rejections occur when the generated trajectory is too long or too short to satisfy the detailed-balance or max-length conditions.

Code	Meaning
`BTL`	Backward trajectory too long — the backward segment exceeded the limit imposed by the detailed-balance condition.
`BTX`	Backward trajectory too long — the backward segment exceeded the hard `maxlength` cut-off.
`BTS`	Backward trajectory too short — the backward segment ended before reaching a required interface.
`FTL`	Forward trajectory too long — the forward segment exceeded the limit imposed by the detailed-balance condition.
`FTX`	Forward trajectory too long — the forward segment exceeded the hard `maxlength` cut-off.
`FTS`	Forward trajectory too short — the forward segment ended before reaching a required interface.
`XSS`	Stone Skipping sub-path too long — an internal sub-path within the Stone Skipping algorithm exceeded the allowed length.

Interface / crossing rejections

Code	Meaning
`NCR`	No crossing with the middle interface — the trial path did not cross the required central interface of the ensemble.
`BWI`	Backward trajectory ends at wrong interface — the backward segment terminated at an interface other than the one required.
`EWI`	Initial path ends at wrong interface — used during path loading/initiation: the loaded path ends at an interface that is not compatible with the ensemble.
`SWI`	Initial path starts at wrong interface — used during path loading/initiation: the loaded path starts at an interface that is not compatible with the ensemble.
`0-L`	{0−} path ends at left interface — for paths in the `{0-}` ensemble the path ended at the left (A-state) interface instead of crossing to the right.
`NSS`	No one-step crossing in Stone Skipping — the Stone Skipping algorithm could not find a valid one-step interface crossing.

Momentum / energy rejections

Code	Meaning
`MCR`	Momenta change rejection — the new momenta drawn during the shooting move were rejected (e.g. by the Metropolis criterion on the kinetic energy).
`KOB`	Kicked outside of boundaries — after the momentum kick the system moved outside the allowed phase-space boundaries.

Detailed-balance / super-detailed-balance rejections

These rejections enforce the (super) detailed-balance conditions for advanced moves.

Code	Meaning
`HAS`	High-acceptance swap rejection — the high-acceptance criterion for Stone Skipping / Wire Fencing detailed balance was not satisfied.
`SSA`	Stone Skipping super-detailed-balance rejection — the Stone Skipping move was rejected by the super-detailed-balance acceptance test.
`WFA`	Wire Fencing super-detailed-balance rejection — the Wire Fencing move was rejected by the super-detailed-balance acceptance test.
`WTA`	Web Throwing super-detailed-balance rejection — the Web Throwing move was rejected by the super-detailed-balance acceptance test.

Target-swap rejections

Code	Meaning
`TSS`	Target swap selection rejection — the target-swap move was rejected at the selection step (no suitable target ensemble was found).
`TSA`	Target swap detailed-balance rejection — the target-swap trial was rejected by the detailed-balance acceptance criterion.

REPPTIS-specific rejections

Code	Meaning
`SWD`	REPPTIS swap — wrong propagation direction — in a REPPTIS swap move the trial trajectory propagated in the wrong direction relative to the interface.
`SWH`	REPPTIS swap — first-half extension rejected — the first half of the REPPTIS swap extension was rejected.

Other

Code	Meaning
`NSG`	No suitable segments — the path contains no segments that can be used as shooting points.
`EXP`	Exploration path — the path was generated during an exploration phase and is not counted as a regular MC step.