multi-task-training.md

Multi-task training

Perform the multi-task training

Training on multiple data sets (each data set contains several data systems) can be performed in multi-task mode, with one common descriptor and multiple specific fitting nets for each data set. One can simply switch the following parameters in training input script to perform multi-task mode:

• {ref}fitting_net <model/fitting_net> --> {ref}fitting_net_dict <model/fitting_net_dict>, each key of which can be one individual fitting net.
• {ref}training_data <training/training_data>, {ref}validation_data <training/validation_data> --> {ref}data_dict <training/data_dict>, each key of which can be one individual data set contains several data systems for corresponding fitting net, the keys must be consistent with those in {ref}fitting_net_dict <model/fitting_net_dict>.
• {ref}loss <loss> --> {ref}loss_dict <loss_dict>, each key of which can be one individual loss setting for corresponding fitting net, the keys must be consistent with those in {ref}fitting_net_dict <model/fitting_net_dict>, if not set, the corresponding fitting net will use the default loss.
• (Optional) {ref}fitting_weight <training/fitting_weight>, each key of which can be a non-negative integer or float, deciding the chosen probability for corresponding fitting net in training, if not set or invalid, the corresponding fitting net will not be used.

The training procedure will automatically choose single-task or multi-task mode, based on the above parameters. Note that parameters of single-task mode and multi-task mode can not be mixed.

An example input for training energy and dipole in water system can be found here: multi-task input on water.

The supported descriptors for multi-task mode are listed:

• {ref}se_a (se_e2_a) <model/descriptor[se_e2_a]>
• {ref}se_r (se_e2_r) <model/descriptor[se_e2_r]>
• {ref}se_at (se_e3) <model/descriptor[se_e3]>
• {ref}se_atten <model/descriptor[se_atten]>
• {ref}hybrid <model/descriptor[hybrid]>

The supported fitting nets for multi-task mode are listed:

• {ref}ener <model/fitting_net[ener]>
• {ref}dipole <model/fitting_net[dipole]>
• {ref}polar <model/fitting_net[polar]>

The output of dp freeze command in multi-task mode can be seen in freeze command.

Initialization from pretrained multi-task model

For advance training in multi-task mode, one can first train the descriptor on several upstream datasets and then transfer it on new downstream ones with newly added fitting nets. At the second step, you can also inherit some fitting nets trained on upstream datasets, by merely adding fitting net keys in {ref}fitting_net_dict <model/fitting_net_dict> and optional fitting net weights in {ref}fitting_weight <training/fitting_weight>.

Take multi-task input on water again for example. You can first train a multi-task model using input script with the following {ref}model <model> part:

    "model": {
        "type_map": ["O", "H"],
        "descriptor": {
            "type":     "se_e2_a",
            "sel":      [46, 92],
            "rcut_smth":    0.5,
            "rcut":     6.0,
            "neuron":       [25, 50, 100],
        },
        "fitting_net_dict": {
            "water_dipole": {
                "type":         "dipole",
                "neuron":       [100, 100, 100],
            },
            "water_ener": {
                "neuron":       [240, 240, 240],
                "resnet_dt":    true,
            }
        },
    }

After training, you can freeze this multi-task model into one unit graph:

$ dp freeze -o graph.pb --united-model

Then if you want to transfer the trained descriptor and some fitting nets (take water_ener for example) to newly added datasets with new fitting net water_ener_2, you can modify the {ref}model <model> part of the new input script in a more simplified way:

    "model": {
        "type_map": ["O", "H"],
        "descriptor": {},
        "fitting_net_dict": {
            "water_ener": {},
            "water_ener_2": {
                "neuron":       [240, 240, 240],
                "resnet_dt":    true,
            }
        },
    }

It will autocomplete the configurations according to the frozen graph.

Note that for newly added fitting net keys, other parts in the input script, including {ref}data_dict <training/data_dict> and {ref}loss_dict <loss_dict> (optionally {ref}fitting_weight <training/fitting_weight>), should be set explicitly. While for old fitting net keys, it will inherit the old configurations if not set.

Finally, you can perform the modified multi-task training from the frozen model with command:

$ dp train input.json --init_frz_model graph.pb

Share layers among energy fitting networks

The multi-task training can be used to train multiple levels of energies (e.g. DFT and CCSD(T)) at the same time. In this situation, one can set {ref}model/fitting_net[ener]/layer_name> to share some of layers among fitting networks. The architecture of the layers with the same name should be the same.

For example, if one want to share the first and the third layers for two three-hidden-layer fitting networks, the following parameters should be set.

"fitting_net_dict": {
    "ccsd": {
        "neuron": [
            240,
            240,
            240
        ],
        "layer_name": ["l0", null, "l2", null]
    },
    "wb97m": {
        "neuron": [
            240,
            240,
            240
        ],
        "layer_name": ["l0", null, "l2", null]
    }
}