feat(model): implement MedianLVQ

README.md

@@ -36,6 +36,7 @@ be available for use in your Python environment as `prototorch.models`.
 - Soft Learning Vector Quantization (SLVQ)
 - Robust Soft Learning Vector Quantization (RSLVQ)
 - Probabilistic Learning Vector Quantization (PLVQ)
+- Median-LVQ
 
 ### Other
 
@@ -51,7 +52,6 @@ be available for use in your Python environment as `prototorch.models`.
 
 ## Planned models
 
-- Median-LVQ
 - Generalized Tangent Learning Vector Quantization (GTLVQ)
 - Self-Incremental Learning Vector Quantization (SILVQ)
 

examples/median_lvq_iris.py

@@ -0,0 +1,52 @@
+"""Median-LVQ example using the Iris dataset."""
+
+import argparse
+
+import prototorch as pt
+import pytorch_lightning as pl
+import torch
+
+if __name__ == "__main__":
+    # Command-line arguments
+    parser = argparse.ArgumentParser()
+    parser = pl.Trainer.add_argparse_args(parser)
+    args = parser.parse_args()
+
+    # Dataset
+    train_ds = pt.datasets.Iris(dims=[0, 2])
+
+    # Dataloaders
+    train_loader = torch.utils.data.DataLoader(
+        train_ds,
+        batch_size=len(train_ds),  # MedianLVQ cannot handle mini-batches
+    )
+
+    # Initialize the model
+    model = pt.models.MedianLVQ(
+        hparams=dict(distribution=(3, 2), lr=0.01),
+        prototypes_initializer=pt.initializers.SSCI(train_ds),
+    )
+
+    # Compute intermediate input and output sizes
+    model.example_input_array = torch.zeros(4, 2)
+
+    # Callbacks
+    vis = pt.models.VisGLVQ2D(data=train_ds)
+    es = pl.callbacks.EarlyStopping(
+        monitor="train_acc",
+        min_delta=0.01,
+        patience=5,
+        mode="max",
+        verbose=True,
+        check_on_train_epoch_end=True,
+    )
+
+    # Setup trainer
+    trainer = pl.Trainer.from_argparse_args(
+        args,
+        callbacks=[vis, es],
+        weights_summary="full",
+    )
+
+    # Training loop
+    trainer.fit(model, train_loader)

prototorch/models/lvq.py

@@ -1,6 +1,8 @@
 """LVQ models that are optimized using non-gradient methods."""
 
 from ..core.losses import _get_dp_dm
+from ..nn.activations import get_activation
+from ..nn.wrappers import LambdaLayer
 from .abstract import NonGradientMixin
 from .glvq import GLVQ
 
@@ -66,4 +68,61 @@ class LVQ21(NonGradientMixin, GLVQ):
 
 
 class MedianLVQ(NonGradientMixin, GLVQ):
-    """Median LVQ"""
+    """Median LVQ
+
+    # TODO Avoid computing distances over and over
+
+    """
+    def __init__(self, hparams, verbose=True, **kwargs):
+        self.verbose = verbose
+        super().__init__(hparams, **kwargs)
+
+        self.transfer_layer = LambdaLayer(
+            get_activation(self.hparams.transfer_fn))
+
+    def _f(self, x, y, protos, plabels):
+        d = self.distance_layer(x, protos)
+        dp, dm = _get_dp_dm(d, y, plabels)
+        mu = (dp - dm) / (dp + dm)
+        invmu = -1.0 * mu
+        f = self.transfer_layer(invmu, beta=self.hparams.transfer_beta) + 1.0
+        return f
+
+    def expectation(self, x, y, protos, plabels):
+        f = self._f(x, y, protos, plabels)
+        gamma = f / f.sum()
+        return gamma
+
+    def lower_bound(self, x, y, protos, plabels, gamma):
+        f = self._f(x, y, protos, plabels)
+        lower_bound = (gamma * f.log()).sum()
+        return lower_bound
+
+    def training_step(self, train_batch, batch_idx, optimizer_idx=None):
+        protos = self.proto_layer.components
+        plabels = self.proto_layer.labels
+
+        x, y = train_batch
+        dis = self.compute_distances(x)
+
+        for i, _ in enumerate(protos):
+            # Expectation step
+            gamma = self.expectation(x, y, protos, plabels)
+            lower_bound = self.lower_bound(x, y, protos, plabels, gamma)
+
+            # Maximization step
+            _protos = protos + 0
+            for k, xk in enumerate(x):
+                _protos[i] = xk
+                _lower_bound = self.lower_bound(x, y, _protos, plabels, gamma)
+                if _lower_bound > lower_bound:
+                    if self.verbose:
+                        print(f"Updating prototype {i} to data {k}...")
+                    self.proto_layer.load_state_dict({"_components": _protos},
+                                                     strict=False)
+                    break
+
+        # Logging
+        self.log_acc(dis, y, tag="train_acc")
+
+        return None