Ascent Utilities

Ascent provides a some utilities to assist users and developers. Currently, Ascent provides two main utilities:

  • : a python program to create a shell script that load libraries built by uberenv (i.e., spack) into the user environment.
  • replay : a set of programs that replays simulation data saved by Ascent or exported by VisIt to Ascent.

Generate Spack Eviromnent Script

The uberenv spack-based build installs libraries into difficult to locate paths. The is a utility program that searches the uberenv build for user specified dependencies and creates shell script that loads these locations into your path.

Why Do I Need This?

Even with a shared library build where dependent library locations are found automatically, some dependencies such as MPI and Python need to be loaded into the user environment for Ascent to execute successfully.

For example if the uberenv built MPI and the user machine also contains an installation of MPI, executing a command such as mpirun -np 4 cloverleaf_par will most definitely invoke the system MPI and not the MPI that Ascent was built with. Mixing MPI versions or implementation will almost never result in successful execution and should be avoided at all costs.

How Do I Use It?

From the top level Ascent directory (i.e., the root of the repository)

python scripts/ mpi conduit python

Simply invoke the script with python followed by a list of packages. In the above example, we are asking program to generate a shell script called to load the paths of mpi, conduit, and python into our environment. Once this command executes, source the shell script to your path:


To verify success, you can echo your path and the paths of the libraries should appear at the front of the path.


Replay is a utility that allows the user to ‘replay’ Conduit Blueprint HDF5 files saved by Ascent or exported by VisIt (starting in version 3.0 beta) back into Ascent. Simulations often take a significant amount of time to develop into a meaningful or interesting state. Replay enables the user or developer to cherry-pick specific time steps and load them into Ascent.

Why Do I Need This?

There are several use cases for using replay:

  • Creating actions files
  • Ascent development
  • Algorithm development

When creating in situ actions, a common strategy for scripting actions a priori is to get a smaller representation of the simulation data a user expects to see in situ and create visualization actions that can then be applied to the full data set in situ. Replay enables the user to load data into Ascent without using a fully integrated simulation workflow.

Additionally, replay can be used for Ascent and algorithm development. Replay can load specific data sets or time steps into Ascent. With replay, loading various test cases and iterating over development cycles is straight forward.

How Do I Get Blueprint Files?

To use replay, you first need compatible data and there are two methods to obtaining it.

Using Ascent

The relay extract saves out Conduit Blueprint HDF5 files that replay consumes. Simply add the extract to the actions in the code or actions file. The relay extract can also sub-select the fields that are saved to reduce the total data set size. For more information see the relay section.

conduit::Node extracts;
extracts["e1/type"]  = "relay";
extracts["e1/params/path"] = "my_output_file_name";
extracts["e1/params/protocol"] = "blueprint/mesh/hdf5";

Using VisIt

Starting with 3.0 beta, VisIt supports exporting databases to the Conduit Blueprint HDF5 format. With this support, VisIt can serve as file format converter from any of the many supported database reader formats to the format that replay can consume.

To export in Blueprint format, select export from VisIt’s File Menu:


Then from the Export to drop-down, select Blueprint:


How Do I Use It?

Replay executables are created in the utilities/replay directory of the installation or build. There are two versions of replay:

  • replay_ser: a serial (non-MPI) version
  • replay_mpi: an MPI version

The options for replay are:

  • --root: specifies Blueprint root file to load
  • --cycles: specifies a text file containing a list of Blueprint root files to load
  • --actions: specifies the name of the actions file to use (default: ascent_actions.json)

Example launches:

./replay_ser --root=clover.cycle_000060.root --actions=my_actions.json
srun -n 8 ./replay_mpi --root=clover.cycle_000060.root --actions=my_actions.json
srun -n 8 ./replay_mpi --cycles=cycles_list.txt --actions=my_actions.json

The cycles files list is a text file containing one root file per line:

cat cycles_list.txt

Replay will loop over these files in the order in which they appear in the file.

Domain Overloading

Each root file can point to any number of domains. When launching replay_mpi, you can specify any number of ranks less than or equal to the number of domains. Replay will automatically domain overload. For example if there were 100 domains and replay is launched with 50 ranks, then each rank will load 2 domains.