Min delta

Intuition

As a neural network accumulates more parameters, it is more exposed to overfitting. Too many epochs can lead to overfitting of the training dataset, whereas too few may result in an underfit model.

A viable solution is to train on the training dataset, but stop training when performance on the validation dataset begins to deteriorate. Early stopping is one such technique that helps in less wastage of training resources. The Keras module contains a built-in callback designed for this purpose called the Early Stopping Callback.

Using tf.keras.callbacks.EarlyStopping, you can implement the Keras API, the high-level API of TensorFlow.

Min delta is an important parameter of the Early Stopping Callback.

If Min delta is set as X, that means the validation accuracy has to improve by at least X for it to count as an improvement.

Code Implementation

PyTorch

      pip install pytorch-ignite
from ignite.engine import Engine, Events
from ignite.handlers import EarlyStopping

def score_function(engine):
    val_loss = engine.state.metrics['nll']
    return -val_loss

handler = EarlyStopping(patience=10, min_delta=0.01, score_function=score_function, trainer=trainer)
# Note: the handler is attached to an *Evaluator* (runs one epoch on validation dataset).
evaluator.add_event_handler(Events.COMPLETED, handler)
    

TensorFlow

      from tensorflow.keras.models import Sequential
from tensorflow.keras.layers import ConviD, Flatten, Dense, MaxPooling1D 
from tensorflow.keras.callbacks import EarlyStopping

model = Sequential([
                    Conv1D(16, 5, activation='relu', input_shape=(128, 1)),
                    MaxPooling 1D(4),
                    Flatten(),
                    Dense(10, activation='softmax')
])

model.compile(optimizer='adam", loss='categorical_crossentropy',metrics=['accuracy'])

early_stopping = EarlyStopping(monitor='val_accuracy', patience-5, min_delta=0.01)

model.fit (X_train, y train, validation_split-0.2, epochs=100,
           callbacks=[early_stopping])
    

Adding the min delta argument to the code implementation in Patience, it creates an argument of the early stopping callback which has been set as 0.01 in this code example. This means that the validation accuracy has to improve by at least 0.01 for it to count as an improvement.

By default, min_delta is zero, which means that any improvement in the performance is enough to reset the patience.