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The History Array

libEnsemble uses a NumPy structured array :ref:`H<datastruct-history-array>` to store corresponding output from each gen_f and sim_f. Similarly, gen_f and sim_f are expected to return output as NumPy structured arrays. The names of the input fields for gen_f and sim_f must be output from gen_f or sim_f. In addition to the user-function output fields, the final history from libEnsemble will include the following:

  • sim_id [int]: Each unit of work output from gen_f must have an associated sim_id. The generator can assign this, but users must be careful to ensure that points are added in order. For example, if alloc_f allows for two gen_f instances to be running simultaneously, alloc_f should ensure that both don’t generate points with the same sim_id.
  • given [bool]: Has this gen_f output been given to a libEnsemble worker to be evaluated yet?
  • given_time [float]: At what time (since the epoch) was this gen_f output given to a worker?
  • sim_worker [int]: libEnsemble worker that output was given to for evaluation
  • gen_worker [int]: libEnsemble worker that generated this sim_id
  • gen_time [float]: At what time (since the epoch) was this entry (or collection of entries) put into H by the manager
  • returned [bool]: Has this worker completed the evaluation of this unit of work?

History and Log Files

The history array :ref:`H<datastruct-history-array>` and :ref:`persis_info<datastruct-persis-info>` dictionary are returned to the user by libEnsemble. If libEnsemble aborts on an exception, these structures are dumped automatically to the respective files:

  • libE_history_at_abort_<sim_count>.npy
  • libE_history_at_abort_<sim_count>.pickle

where sim_count is the number of points evaluated. To suppress libEnsemble from producing these two files, set libE_specs['save_H_and_persis_on_abort'] to False.

Two other libEnsemble files produced by default:

  • libE_stats.txt: This contains one-line summaries for each user calculation. Each summary is sent by workers to the manager and logged as the run progresses.
  • ensemble.log: This contains logging output from libEnsemble. The default logging level is INFO. In order to gain additional diagnostics, the logging level can be set to DEBUG. If this file is not removed, multiple runs will append output. Messages at or above MANAGER_WARNING are also copied to stderr to alert the user promptly. For more info, see :doc:`Logging<logging>`.

To suppress libEnsemble from producing these two files, set libE_specs['disable_log_files'] to True.

Output Working Directory Structure

libEnsemble features configurable output and working directory structuring for storing results at every step of a calculation, or directing workers to perform calculations on separate filesystems or in other directories. This is helpful for users performing simulations who want to take advantage of high-speed scratch spaces or disks, or organize their I/O by application run.

With these features enabled, each time a worker initiates a simulation routine it automatically enters a configurable directory, either a new directory specific to that worker and simulation instance or a shared directory for all workers. Where these directories are created or what files they contain is configurable through settings in :ref:`libE_specs<datastruct-libe-specs>`. Defining any compatible settings initiates this system with default settings for unspecified options. Each setting will be described in detail here:

  • 'sim_dirs_make': Boolean. Enables per-simulation directories with default settings. Directories are labeled in the form 'sim0-worker1' and without further configuration, placed in the ensemble directory ./ensemble, relative to where libEnsemble was launched. Default: True. If False, all workers will operate within the ensemble directory without producing per-simulation directories.

  • 'ensemble_dir_path': This location, typically referred to as the ensemble directory, is where each worker places its simulation directories. If not specified, simulation directories are placed in ./ensemble, relative to where libEnsemble was launched. If 'sim_dirs_make' is False, all workers will run within this directory. On supported systems, writing to local-node storage is possible and recommended for increased performance.:

    libE_specs['ensemble_dir_path'] = "/scratch/my_ensemble"

  • 'use_worker_dirs': Boolean. Sorts simulation directories into per-worker directories at runtime. Particularly useful for organization when running with multiple workers on global scratch spaces or the same node, and may produce performance benefits. Default: False.

    Default structure with 'use_worker_dirs' unspecified:

    - /ensemble_dir
    - /sim0-worker1
    - /sim1-worker2
    ...

    Structure with libE_specs['use_worker_dirs'] = True:

    - /ensemble_dir
    - /worker1
        - /sim0
        - /sim4
        ...
    - /worker2
    ...

  • 'sim_dir_copy_files': A list of paths for files to copy into simulation directories. If 'sim_dirs_make' is False, these files are copied to the ensemble directory. If using the :ref:`Executor<executor_index>` to launch an application, this may be helpful for copying over configuration files for each launch.

  • 'sim_dir_symlink_files': A list of paths for files to symlink into simulation directories.

  • 'ensemble_copy_back': Boolean. Instructs the manager to create an empty directory where libEnsemble was launched where workers copy back their simulation directories on a run's conclusion or an exception. Especially useful when 'ensemble_dir_path' has been set to some scratch space or another temporary location. Default: False.

  • 'sim_input_dir': A path to a directory to copy for simulation directories. This directory and it's contents are copied to form the base of new simulation directories. If 'sim_dirs_make' is False, this directory's contents are copied into the ensemble directory.

See the regression tests test_sim_dirs_per_calc.py and test_use_worker_dirs.py for examples of many of these settings. See test_sim_input_dir_option.py for examples of using these settings without simulation-specific directories.

Note

The postproc_scripts directory, in the libEnsemble project root directory, contains scripts to compare outputs and create plots based on the ensemble output.