WARNING: API is not yet stable, expect breaking changes in 0.x versions!

To install, just do:

pip install dnn_cool

• Introduction: What is dnn_cool in a nutshell?
• Examples: a simple step-by-step example.
• Features: a list of the utilities that dnn_cool provides for you
• Customization: Learn how to add new tasks, modify them, etc.
• Inspiration: list of papers and videos which inspired this library

To see the predefined tasks for this release, see list of predefined tasks

A framework for multi-task learning in Pytorch, where you may precondition tasks and compose them into bigger tasks. Many complex neural networks can be trivially implemented with dnn_cool. For example, creating a neural network that does classification and localization is as simple as:

@project.add_flow
def localize_flow(flow, x, out):
    out += flow.obj_exists(x.features)
    out += flow.obj_x(x.features) | out.obj_exists
    out += flow.obj_y(x.features) | out.obj_exists
    out += flow.obj_w(x.features) | out.obj_exists
    out += flow.obj_h(x.features) | out.obj_exists
    out += flow.obj_class(x.features) | out.obj_exists
    return out

If for example you want to classify first if the camera is blocked and then do localization given that the camera is not blocked, you could do:

@project.add_flow
def full_flow(flow, x, out):
    out += flow.camera_blocked(x.cam_features)
    out += flow.localize_flow(x.localization_features) | (~out.camera_blocked)
    return out

Based on these "task flows" as we call them, dnn_cool provides a bunch of features. Currently, this is the list of the predefined tasks (they are all located in dnn_cool.task_flow):

In the current release, the following tasks are available out of the box:

• BinaryClassificationTask - sigmoid activation, thresholding decoder, binary cross entropy loss function. In the examples above, camera_blocked and obj_exists are BinaryClassificationTasks.
• ClassificationTask - softmax activation, sorting classes decoder, categorical cross entropy loss. In the example above, obj_class is a ClassificationTask
• MultilabelClassificationTask - sigmoid activation, thresholding decoder, binary cross entropy loss function.
• BoundedRegressionTask - sigmoid activation, rescaling decoder, mean squared error loss function. In the examples above, obj_x, obj_y, obj_w, obj_h are bounded regression tasks.
• MaskedLanguageModelingTask - softmax activation, sorting decoder, cross entropy per token loss.
• TaskFlow - a composite task, that contains a list of children tasks. We saw 2 task flows above.

We just have to add a ClassificationTask named classifier and add the flow below:

@project.add_flow()
def imagenet_model(flow, x, out):
    out += flow.classifier(x.features)
    return out

That's great! But what if there is not an object always? Then we have to first check if an object exists. Let's add a BinaryClassificationTask and use it as a precondition to classifier.

@project.add_flow()
def imagenet_model(flow, x, out):
    out += flow.object_exists(x.features)
    out += flow.classifier(x.features) | out.object_exists
    return out

But what if we also want to localize the object? Then we have to add new tasks that regress the bounding box. Let's call them object_x, object_y, object_w, object_h and make them a BoundedRegressionTask. To avoid preconditioning all tasks on object_exists, let's group them first. Then we modify the flow:

@project.add_flow()
def object_flow(flow, x, out):
    out += flow.classifier(x.features)
    out += flow.object_x(x.features)
    out += flow.object_y(x.features)
    out += flow.object_w(x.features)
    out += flow.object_h(x.features)
    return out 

@project.add_flow()
def imagenet_flow(flow, x, out):
    out += flow.object_exists(x.features)
    out += flow.object_flow(x.features) | out.object_exists
    return out

But what if the camera is blocked? Then there is no need to do anything, so let's create a new flow that executes our imagenet_flow only when the camera is not blocked.

def full_flow(flow, x, out):
    out += flow.camera_blocked(x.features)
    out += flow.imagenet_flow(x.features) | (~out.camera_blocked)
    return out

But what if for example we want to check if the object is a kite, and if it is, to classify its color? Then we would have to modify our object_flow as follows:

@project.add_flow()
def object_flow(flow, x, out):
    out += flow.classifier(x.features)
    out += flow.object_x(x.features)
    out += flow.object_y(x.features)
    out += flow.object_w(x.features)
    out += flow.object_h(x.features)
    out += flow.is_kite(x.features)
    out += flow.color(x.features) | out.is_kite
    return out 

I think you can see what dnn_cool is meant to do! :)

To see a full walkthrough on a synthetic dataset, check out the Colab notebook or the markdown write-up.

Main features are:

• Task precondition
• Missing values handling
• Task composition
• Tensorboard metrics logging
• Task interpretations
• Task evaluation
• Task threshold tuning
• Dataset generation
• Tree explanations
• Memory balancing for dataparallel

Use the | for task preconditioning (think of P(A|B) notation). Preconditioning - A | B means that:

• Include the ground truth for B in the input batch when training
• When training, update the weights of the A only when B is satisfied in the ground truth.
• When training, compute the loss function for A only when B is satisfied in the ground truth
• When training, compute the metrics for A only when B is satisfied in the ground truth.
• When tuning threshold for A, optimize only on values for which B is satisfied in the ground truth.
• When doing inference, compute the metrics for A only when the precondition is satisfied according to the decoded result of the B task
• When generating tree explanation in inference mode, do not show the branch for A if B is not satisfied.
• When computing results interpretation, include only loss terms when the precondition is satisfied.

Usually, you have to keep track of all this stuff manually, which makes adding new preconditions very difficult. dnn_cool makes this stuff easy, so that you can chain a long list of preconditions without worrying you forgot something.

Sometimes for an input you don't have labels for all tasks. With dnn_cool, you can just mark the missing label and dnn_cool will update only the weights of the tasks for which labels are available.

This feature has the awesome property that you don't need a single dataset with all tasks labeled, you can have different datasets for different tasks and it will work. For example, you can train a single object detection neural network that trains its classifier head on ImageNet, and its detection head on COCO.

You can group tasks in a task flow (we already saw 2 above - localize_flow and full_flow). You can use this to organize things better, for example when you want to precondition a whole task flow. For example:

@project.add_flow
def face_regression(flow, x, out):
    out += flow.face_x1(x.face_localization)
    out += flow.face_y1(x.face_localization)
    out += flow.face_w(x.face_localization)
    out += flow.face_h(x.face_localization)
    out += flow.facial_characteristics(x.features)
    return out

dnn_cool logs the metrics per task in Tensorboard, e.g:

Also, the best and worst inputs per task are logged in the Tensorboard, for example if the input is an image:

Per-task evaluation information is available, to pinpoint the exact problem in your network. An example evaluation dataframe:

Many tasks need to tune their threshold. Just call flow.get_decoder().tune() and you will get optimized thresholds for the metric you define.

As noted above, dnn_cool will automatically trace the tasks used as a precondition and include the ground truth for them under the key gt.

Examples:

├── inp 1
│   └── camera_blocked | decoded: [False], activated: [0.], logits: [-117.757324]
│       └── door_open | decoded: [ True], activated: [1.], logits: [41.11258]
│           └── person_present | decoded: [ True], activated: [1.], logits: [60.38873]
│               └── person_regression
│                   ├── body_regression
│                   │   ├── body_h | decoded: [29.672623], activated: [0.46363473], logits: [-0.14571853]
│                   │   ├── body_w | decoded: [12.86382], activated: [0.20099719], logits: [-1.3800735]
│                   │   ├── body_x1 | decoded: [21.34288], activated: [0.3334825], logits: [-0.69247603]
│                   │   ├── body_y1 | decoded: [18.468979], activated: [0.2885778], logits: [-0.9023013]
│                   │   └── shirt_type | decoded: [6 1 0 4 2 5 3], activated: [4.1331367e-23 3.5493638e-17 3.1328378e-26 5.6903808e-30 2.4471377e-25
 2.8071076e-29 1.0000000e+00], logits: [-20.549513  -6.88627  -27.734364 -36.34787  -25.6788   -34.751904
  30.990908]
│                   └── face_regression
│                       ├── face_h | decoded: [11.265154], activated: [0.17601803], logits: [-1.5435623]
│                       ├── face_w | decoded: [12.225838], activated: [0.19102871], logits: [-1.4433397]
│                       ├── face_x1 | decoded: [21.98834], activated: [0.34356782], logits: [-0.64743483]
│                       ├── face_y1 | decoded: [3.2855165], activated: [0.0513362], logits: [-2.9166584]
│                       └── facial_characteristics | decoded: [ True False  True], activated: [9.9999940e-01 1.2074912e-12 9.9999833e-01], logits: [ 14.240071 -27.442476  13.27557 ]

but if the model thinks the camera is blocked, then the explanation would be:

├── inp 2
│   └── camera_blocked | decoded: [ True], activated: [1.], logits: [76.367676]

When using nn.DataParallel, the computation of the loss function is done on the main GPU, which leads to dramatically unbalanced memory usage if your outputs are big and you have a lot of metrics (e.g segmentation masks, language modeling, etc). dnn_cool gives you a convenient way to balance the memory in such situations - just a single balance_dataparallel_memory = True handles this case for you by first reducing all metrics on their respective device, and then additionally aggregating the results that were reduced on each device automatically. Here's an example memory usage:

Before:

After:

Since flow.torch() returns a normal nn.Module, you can use any library you are used to. If you use Catalyst, dnn_cool provides a bunch of useful callbacks. Creating a new task is as simple as creating a new instance of this dataclass:

@dataclass
class Task(ITask):
    name: str
    labels: Any
    loss: nn.Module
    per_sample_loss: nn.Module
    available_func: Callable
    inputs: Any
    activation: Optional[nn.Module]
    decoder: Decoder
    module: nn.Module
    metrics: Tuple[str, TorchMetric]

Alternatively, you can subclass ITask and implement its inferface.

• Andrej Karpathy: Tesla Autopilot and Multi-Task Learning for Perception and Prediction
• PyTorch at Tesla - Andrej Karpathy, Tesla
• Multitask learning - Andrew Ng