[ENH] Add AEBiGRUNetwork (#1583)

* Add AEBiGRUNetwork

* Add path to init

* minor

* Add temporal latent space kwarg

* Add tests and minor fixes

* minor

* pre-commit

* refactor tests

* add tag

* fix bugs

* update base

* minor

* minor

aeon/networks/__init__.py

@@ -13,7 +13,9 @@
     "AEFCNNetwork",
     "AEResNetNetwork",
     "LITENetwork",
+    "AEBiGRUNetwork",
 ]
+from aeon.networks._ae_bgru import AEBiGRUNetwork
 from aeon.networks._ae_fcn import AEFCNNetwork
 from aeon.networks._ae_resnet import AEResNetNetwork
 from aeon.networks._cnn import CNNNetwork

aeon/networks/_ae_bgru.py

@@ -0,0 +1,142 @@
+"""Implement Auto-Encoder based on Bidirectional GRUs."""
+
+from aeon.networks.base import BaseDeepLearningNetwork
+
+
+class AEBiGRUNetwork(BaseDeepLearningNetwork):
+    """
+    A class to implement an Auto-Encoder based on Bidirectional GRUs.
+
+    Parameters
+    ----------
+        latent_space_dim : int, default=128
+            Dimension of the latent space.
+        n_layers : int, default=None
+            Number of BiGRU layers. If None, defaults will be used.
+        n_units : list
+            Number of units in each BiGRU layer. If None, defaults will be used.
+        activation : Union[list, str]
+            Activation function(s) to use in each layer.
+            Can be a single string or a list.
+        temporal_latent_space : bool, default = False
+            Flag to choose whether the latent space is an MTS or Euclidean space.
+    """
+
+    _config = {
+        "python_dependencies": ["tensorflow"],
+        "python_version": "<3.12",
+        "structure": "encoder",
+    }
+
+    def __init__(
+        self,
+        latent_space_dim=128,
+        n_layers=None,
+        n_units=None,
+        activation="relu",
+        temporal_latent_space=False,
+    ):
+        super().__init__()
+
+        self.latent_space_dim = latent_space_dim
+        self.activation = activation
+        self.n_layers = n_layers
+        self.n_units = n_units
+        self.temporal_latent_space = temporal_latent_space
+
+    def build_network(self, input_shape, **kwargs):
+        """Construct a network and return its input and output layers.
+
+        Parameters
+        ----------
+        input_shape : tuple of shape = (n_timepoints (m), n_channels (d))
+            The shape of the data fed into the input layer.
+
+        Returns
+        -------
+        encoder : a keras Model.
+        decoder : a keras Model.
+        """
+        import tensorflow as tf
+
+        if self.n_layers is None:
+            if self.n_units is not None:
+                raise ValueError(
+                    """Cannot pass number of units without specifying
+                            number of layers."""
+                )
+            elif self.n_units is None:
+                self._n_layers, self._n_units = 2, [50, self.latent_space_dim // 2]
+        elif self.n_layers is not None:
+            self._n_layers = self.n_layers
+            if self.n_units is None:
+                self._n_units = [50 for _ in range(self.n_layers)]
+                self._n_units[-1] = self.latent_space_dim // 2
+            elif self.n_units is not None:
+                if isinstance(self.n_units, list):
+                    self._n_units = self.n_units
+                    self._n_units[-1] = self.latent_space_dim // 2
+                    assert len(self.n_units) == self.n_layers
+                elif isinstance(self.n_units, int):
+                    self._n_units = [self.n_units for _ in range(self.n_layers)]
+                    self._n_units[-1] = self.latent_space_dim // 2
+
+        if isinstance(self.activation, str):
+            self._activation = [self.activation for _ in range(self._n_layers)]
+        else:
+            self._activation = self.activation
+            assert isinstance(self.activation, list)
+            assert len(self.activation) == self._n_layers
+
+        encoder_inputs = tf.keras.layers.Input(shape=input_shape, name="encoder_input")
+        x = encoder_inputs
+        for i in range(self._n_layers):
+            return_sequences = i < self._n_layers - 1
+            if self.temporal_latent_space:
+                return_sequences = i < self._n_layers
+            x = tf.keras.layers.Bidirectional(
+                tf.keras.layers.GRU(
+                    units=self._n_units[i],
+                    activation=self._activation[i],
+                    return_sequences=return_sequences,
+                ),
+                name=f"encoder_bgru_{i+1}",
+            )(x)
+
+        latent_space = tf.keras.layers.Dense(
+            self.latent_space_dim, activation="linear", name="latent_space"
+        )(x)
+        encoder_model = tf.keras.models.Model(
+            inputs=encoder_inputs, outputs=latent_space, name="encoder"
+        )
+
+        if not self.temporal_latent_space:
+            decoder_inputs = tf.keras.layers.Input(
+                shape=(self.latent_space_dim,), name="decoder_input"
+            )
+            x = tf.keras.layers.RepeatVector(input_shape[0], name="repeat_vector")(
+                decoder_inputs
+            )
+        elif self.temporal_latent_space:
+            decoder_inputs = tf.keras.layers.Input(
+                shape=latent_space.shape[1:], name="decoder_input"
+            )
+            x = decoder_inputs
+
+        for i in range(self._n_layers - 1, -1, -1):
+            x = tf.keras.layers.Bidirectional(
+                tf.keras.layers.GRU(
+                    units=self._n_units[i],
+                    activation=self._activation[i],
+                    return_sequences=True,
+                ),
+                name=f"decoder_bgru_{i+1}",
+            )(x)
+        decoder_outputs = tf.keras.layers.TimeDistributed(
+            tf.keras.layers.Dense(input_shape[1]), name="decoder_output"
+        )(x)
+        decoder_model = tf.keras.models.Model(
+            inputs=decoder_inputs, outputs=decoder_outputs, name="decoder"
+        )
+
+        return encoder_model, decoder_model

aeon/networks/tests/test_ae_bgru.py

@@ -0,0 +1,54 @@
+"""Tests for the AEBiGRU Model."""
+
+import random
+
+import pytest
+
+from aeon.networks import AEBiGRUNetwork
+from aeon.utils.validation._dependencies import _check_soft_dependencies
+
+
+@pytest.mark.skipif(
+    not _check_soft_dependencies(["tensorflow"], severity="none"),
+    reason="Tensorflow soft dependency unavailable.",
+)
+@pytest.mark.parametrize(
+    "latent_space_dim,n_layers,temporal_latent_space",
+    [
+        (32, 1, True),
+        (128, 2, False),
+        (256, 3, True),
+        (64, 4, False),
+    ],
+)
+def test_aebigrunetwork_init(latent_space_dim, n_layers, temporal_latent_space):
+    """Test whether AEBiGRUNetwork initializes correctly for various parameters."""
+    aebigru = AEBiGRUNetwork(
+        latent_space_dim=latent_space_dim,
+        n_layers=n_layers,
+        temporal_latent_space=temporal_latent_space,
+        activation=random.choice(["relu", "tanh"]),
+        n_units=[random.choice([50, 25, 100]) for _ in range(n_layers)],
+    )
+    encoder, decoder = aebigru.build_network((1000, 5))
+    assert encoder is not None
+    assert decoder is not None
+
+
+@pytest.mark.skipif(
+    not _check_soft_dependencies(["tensorflow"], severity="none"),
+    reason="Tensorflow soft dependency unavailable.",
+)
+@pytest.mark.parametrize("activation", ["relu", "tanh"])
+def test_aebigrunetwork_activations(activation):
+    """Test whether AEBiGRUNetwork initializes correctly with different activations."""
+    aebigru = AEBiGRUNetwork(
+        latent_space_dim=64,
+        n_layers=2,
+        temporal_latent_space=True,
+        activation=activation,
+        n_units=[50, 50],
+    )
+    encoder, decoder = aebigru.build_network((1000, 5))
+    assert encoder is not None
+    assert decoder is not None