ensemble_generator

The ensemble_generator test group (compass.landice.tests.ensemble_generator) creates an ensemble of MALI simulations with different parameter values. The ensemble framework sets up a user-defined number of simulations with parameter values selected from a space-filling Sobol sequence (see ensemble_generator).

framework

The shared config options for the ensemble_generator test group are described in ensemble_generator in the User’s Guide. See the thwaites test case description below for how this framework should be used to set up an ensemble.

ensemble_member

The class compass.landice.tests.ensemble_generator.EnsembleMember defines a step for a single ensemble member (model run). The constructor stores the run number and name, as well as the parameter values to be used and the python package where the namelist, streams, and albany input file can be found. By setting up an ensemble_member this way, this class can be flexibly called from any test case that one would like to define.

The setup method actually sets up the run by first setting up a baseline configuration and then modifying parameter values using the parameter values defined when the constructor was called. There are operations to set parameters:

  • basal friction exponent

  • von Mises threshold stress

  • calving speed limit

  • gamma0 melt sensitivity parameter in ISMIP6-AIS ice-shelf basal melting parameterization

  • deltaT thermal forcing bias adjustment parameter in ISMIP6-AIS ice-shel basal melting parameterization

These parameter values are always set; if it is desired they not be modified from the baseline configuration, a default value should be passed to the constructor from the test case calling this class, e.g., compass.landice.tests.ensemble_generator.thwaites.ThwaitesEnsemble.

Because changing the exponent requires modifying the input file to adjust muFriction to yield the same basal shear stress as the original file, there is also an operation to set the output filename in the streams file, where the file to be used and modified was specified in the cfg file for the test case. The default input file is renamed to indicate the updated exponent value it is appropriate for. This is updated automatically in the streams file, but it avoids potential confusion if a user were to use this file for another purpose.

Similarly, because changing gamma0 and deltaT require modifying a basal melt parameter file, the baseline file path needs to be specified in the config and that file is copied, renamed, and modified in each run directory.

Additionally, a job script is written for the run so that the run can be submitted as a slurm job independent of other runs in the ensemble. This also allows a user to easily run a single ensemble member by submitting the job script within the run step work directory.

Finally, a symlink to the compass load script is added to the run work directory, which compass does not do by default.

The run method creates a graph file and runs MALI.

Finally, there is a function _adjust_friction_exponent that modifies the friction exponent in the albany_input.yaml file and adjusts muFriction in the input file to maintain an unchanged basal shear stress. Similarly, there is a function _adjust_basal_melt_params that modifes gamma0 and deltaT in a basal melt parameter file.

ensemble_manager

The class compass.landice.tests.ensemble_generator.EnsembleManager defines a step for managing the entire ensemble. The constructor and setup methods perform minimal operations. The run method submits each run in the ensemble as a slurm job. Eventually the ensemble_manager will be able to assess if runs need restarts and modify them to be submitted as such.

thwaites

The compass.landice.tests.ensemble_generator.thwaites.ThwaitesEnsemble uses the framework described above to set up an ensemble of Thwaites Glacier simulations. The constructor simply adds the ensemble manager as the only step. This allows the test case to be listed by compass list without having all ensemble members listed in a verbose listing. Because there may be dozens of ensemble members, it is better to wait to have them added until the setup phase. Also, by waiting until configure to define the ensemble members, it is possible to have the start and end run numbers set in the config, because the config is not parsed by the constructor.

The configure method is where most of the work happens. Here, the start and end run numbers are read from the config, the parameter array is read from file, and the parameters to be varied and over what range is defined. Basal friction exponent and von Mises threshold stress are varied over set ranges. The calving speed limit is set to a fixed value for all runs, but could be included as a varying parameter in the future. The values for each parameter are passed to the EnsembleMember constructor to define each run. Finally, each run is now added to the test case as a step to run, because they were not automatically added by compass during the test case constructor phase.

Note, the configure method could be modified to use other parameter value sampling techniques than the provided 2d Sobol sequence. For example, a sensitivity test could be performed by defining one parameter’s values using the numpy arange function or similar.

There are no run or validate steps required. The ensemble manager handles “running” ensemble members by submitting them as slurm jobs. This is a major difference in how this test case functions from most compass test cases. The visualization script plot_ensemble.py is symlinked in the test case work directory and can be run manually to assess the status of the ensemble, but there is not a formal analysis step that can be run through compass.