{
    "save_path": "./sand3d_collision/",
      "output_format": {  # Optional
        "timestep_downsampling_rate": 2,  # Downsample timestep, else, default is set to 1.0
        "material_feature": [  # Choose what material feature to include in the input npz
            "friction_angle",
            "elastic_modulus"
        ]
    },
    "id_range": [  # the id of simulations to generate
        0,
        10
    ],
    "domain_size": 1.0,  # the largest domain length (same for all dimension)
    "friction_angle": 35,
    "wall_friction": 0.43,
    "elastic_modulus": 2000000.0,
    "poisson_ratio": 0.3,
    "rho": 1800,
    "sim_space": [  # lower and upper boundary for each dimension 
        [
            0.2,
            0.8
        ],
        [
            0.2,
            0.8
        ],
        [
            0.2,
            0.8
        ]
    ],
    "sim_resolution": [
        32,
        32,
        32
    ],
    "nsteps": 350,  # number of forward steps
    "mpm_dt": 0.0025,  # time between forward steps
    "gravity": [0, -9.81, 0],
    "gen_cube_randomly": {
        "generate": true,
        "sim_inputs": {
            "mass": {
                "ncubes": [1, 2],
                "min_distance_between_cubes": 0.01,
                "cube_size_range": [[0.15, 0.3], [0.15, 0.3], [0.15, 0.3]],
                "cube_gen_space": [[0.11, 0.5], [0.11, 0.50], [0.11, 0.89]],
                "vel_range": [[3, 3], [-2.5, 2.5], [-2.5, 2.5]],
                "nparticle_limits": 15000
            },
            "obstacles": {
                "ncubes": [1, 2],
                "min_distance_between_cubes": 0.01,
                "cube_size_range": [[0.1, 0.1], [0.3, 0.3], [0.1, 0.1]],
                "cube_gen_space": [[1.0, 1.5], [0.10, 0.4], [0.15, 0.85]],
                "nparticle_limits": 7000
            }
        }
    },
    "gen_cube_from_data": {
        "generate": true,
        "sim_inputs": [
            {
                "id": 0,  # id of simulation
                "mass": {
                    "cubes": [
                        [
                            0.2,  # x corner 
                            0.2,  # y corner
                            0.2,  # z corner
                            0.2,  # x length
                            0.3,  # y length
                            0.4   # z length 
                        ],
                        "parcitles.csv"  # custom particle data
                    ],
                    "velocity_for_cubes": [
                        [
                            1.0,  # x vel
                            1.0,  # y vel
                            1.5   # z vel
                        ],
                        [
                             1.0, 
                             0.0,
                             -0.5   
                        ]
                    ]
                },
                "obstacles": null  # may repeat the as what is written in "mass" to add obstacles
            },
            {
              "id": 1  
                ...  # may repeat that is written in id 0 to add more simulations
            }
        ]
    },
    "visualization": {
        "is_realtime_vis": false,
        "is_save_animation": true,
        "skip": 1
    }
}