How to roughly control ADIOS2 block number and WarpX particle number

[Change72]

1. ADIOS2 block number:

I want to increase the ADIOS2 block number. I notice the field number is matched with grids number. For example, key = /data/600/fields/E/x. However, for particle blockNum, it seems a magic number: key = /data/600/particles/electrons/momentum/x. I didn't find any parameter to control it, and I guess there should be one in the openPMD layer.

n_cell	max_grid_size	blocking_factor	grids	field blockNum	particle blockNum	smallest grid	biggest grid
32x32x256	64	32	4	4	128	32x32x64	32x32x64
256x256x512	64	32	128	128	128	64x64x64	64x64x64
64x64x256	64	32	4	4	4	64x64x64	64x64x64
256x256x256	8	8	32768	32768	738	8x8x8	8x8x8

    bpIO = adios.DeclareIO("ReadBP");
    bpIO.SetParameter("Threads", std::to_string(nThreads));
    bpReader = bpIO.Open(bpFileName, adios2::Mode::Read);

    adios2::Variable<double> x_meta_info = bpIO.InquireVariable<double>(key + "x");
    auto xBlocksInfo = bpReader.AllStepsBlocksInfo(x_meta_info);
    auto x_it = xBlocksInfo.begin();
    
    for (; x_it != xBlocksInfo.end(); ++x_it) {
        const auto &var_vec1 = x_it->second;
        std:cout << var_vec1.size() << std::endl;  // as ADIOS2 block number
    }

2. for the particle number in bpls, the injection style I used is electrons.injection_style = "NRandomPerCell". The first two lines satisfy the exception, but the third and fourth lines are quite weird.

n_cell	iteration	num_particles_per_cell	num_particles_in_last_iteration
32x32x256	500	1	116072
32x32x256	500	100	11607258
256x256x512	600	100	14069550
64x64x256	600	10000	45020389
256x256x256	600	1	64950

[ax3l]

@guj do you want to comment first? :)

[guj]

Sorry I missed this one.

For 1, yes, the number of ADIOS blocks for field related variables equals the number of sub grids. Looks like you know how to adjust number of sub grids via blocking factor/max_grid_size. I am aware of any way to predict number of blocks for particles. @ax3l can comment.

The keys you mentioned are names of ADIOS variables. Looks like you are using openPMD's group based outputs, so the time steps are embedded in the names. It has no relation with number of blocks.

For 2, Sorry I am not sure I understand the question. Maybe @ax3l can help.

[Change72]

@ax3l any idea? :)