Highlights of What’s New in Version 2020.4

Here is a summary of what’s changed since release 2020.3.

The TAPERAPC element would mark all particles as lost when the RSTART and REND parameters had the same value. This was reported by forum user Cai_Meng.
The FMULT element had a bug that produced very invalid results with the FSE parameter was non-zero, as reported by A. Xiao (APS). Also, the FSE and other parameters were not influencing matrix-related computations if changed during a run.
Use of the XREADOUT and YREADOUT features of the MONI element resulted in a message about undefined rpn variables.

The load_parameters command produced incorrect results in multi-step runs (i.e., n_steps¿1 in run_control) when a multi-page parameter file was used with multiple differential-mode load instructions for the same element. This was reported by V. Sajaev (APS).
The HKICK, VKICK, and HVKICK elements were not responding properly to the ramp_elements and modulate_elements commands. This was reported by V. Sajaev (APS).
A bug was fixed in ion_effects that sometimes caused unphysical sigma values in the bi- and tri-gaussian fits. The bug was found and fixed by J. Calvey (APS).
A bug was fixed that resulted in a crash when coupled=1 was set for trajectory response matrix output from correction_matrix_output.
A bug was fixed that resulted in a crash if a beamline definition contained unbalanced quotation marks. This was reported by X. Huang (APS).

The CCBEND, CSBEND, FMULT, KOCT, KSEXT, and KQUAD now support sixth-order symplectic integrators. The coefficients were provided by Y.P. Sun (APS), who also assisted in testing. The value of the N_KICKS parameter may be reduced by a factor of ~5 if the sixth-order integrator is used in place of the fourth-order integrator, with essentially identical results but a ~30% reduction in run time.
The APCONTOUR element has two new parameters: STICKY and CANCEL. The STICKY parameter results in the aperture contour being applied inside subsequent CCBEND, CSBEND, CSRCSBEND, KQUAD, KSEXT, verb—KOCT—, and KQUSE elements, as well as at the end of other downstream elements. This continues until another APCONTOUR element asserts a new contour, or uses CANCEL=1 to cancel the feature. This improvement was inspired by forum user dondreka.

Added bpm_centroid parameter to the run_setup command. This provides a facility similar to the centroid parameter, but instead of giving the centroids at all elements, it gives them at the BPMs only. This was requested by X. Huang (APS).
The moments_output command now provides additional quantities for optimization at MARK locations. See the documentation for the MARK element.
The modulate_elements command now provides the ability to use the pass number to compute the time, which is helpful in simulations where the time is offset by CHANGE_T=1 on RFCA elements.
Several improvements were made to the ion_effects command by J. Calvey (APS). The gaussianfit option was added for the field_calculation_method parameter; this provides a gaussian fit to model the ion fields, as an alternative to using gaussian statistics or more complex fitting functions. Also, a new parameter, ion_output_interval, was added that allows increasing the interval between logging of ion data.
The correct command accepts a new value, coupled, for the method parameter when mode is trajectory. This allows trajectory correction in strongly-coupled transport lines.
The bunched_beam_moments command was added. This command is virtually identical to the venerable bunched_beam command, but instead of specifying the beam dimensions in terms of emittances, beta functions, etc., the user provides beam moments (e.g., beam size, divergence, etc.).

The population_log file produced by parallel_optimization_setup erroneously recorded the values of the optimization variables in the wrong in an offset fashion.