User interface

[rodrigo-ceccato]

We have to decide on a user interface to leverage application parameters; JSON may not be the best representation for human-writing;

[rodrigo-ceccato]

We need a way for the user to specify valid input combinations, like:

    "mpi-io": {
        "nodes": [
            1,
            2
        ],
        "procs": [
            1
        ],
        "read_step": [
            100
        ]
    }

But say that 2 nodes with 1 proc does not make sense.