Disable temperature scaling during training.

For the `GaussianProcessClassificationHead`, the temperature scaling needs to be disabled during training to avoid unexpected modification to the learning rate, which harms model quality. (Unfortunately, this seems to require adding `training` to the `call` method).

Also set the default of `gp_cov_ridge_penalty` in `RandomFeatureGaussianProcess` to 1 to be consistent with that in the `GaussianProcessClassificationHead`.

PiperOrigin-RevId: 366917075

official/nlp/modeling/layers/cls_head.py

@@ -252,11 +252,15 @@ class GaussianProcessClassificationHead(ClassificationHead):
           name="logits",
           **self.gp_layer_kwargs)
 
-  def call(self, features, return_covmat=False):
+  def call(self, features, training=False, return_covmat=False):
     """Returns model output.
 
+    Dring training, the model returns raw logits. During evaluation, the model
+    returns uncertainty adjusted logits, and (optionally) the covariance matrix.
+
     Arguments:
       features: A tensor of input features, shape (batch_size, feature_dim).
+      training: Whether the model is in training mode.
       return_covmat: Whether the model should also return covariance matrix if
         `use_gp_layer=True`. During training, it is recommended to set
         `return_covmat=False` to be compatible with the standard Keras pipelines
@@ -276,13 +280,13 @@ class GaussianProcessClassificationHead(ClassificationHead):
     else:
       covmat = None
 
-    # Computes the uncertainty-adjusted logits.
+    # Computes the uncertainty-adjusted logits during evaluation.
+    if not training:
       logits = gaussian_process.mean_field_logits(
           logits, covmat, mean_field_factor=self.temperature)
 
     if return_covmat and covmat is not None:
       return logits, covmat
-
     return logits
 
   def reset_covariance_matrix(self):

official/nlp/modeling/layers/cls_head_test.py

@@ -134,7 +134,6 @@ class GaussianProcessClassificationHead(tf.test.TestCase,
         num_classes=num_classes,
         use_spec_norm=True,
         use_gp_layer=use_gp_layer,
-        initializer="zeros",
         **self.spec_norm_kwargs,
         **self.gp_layer_kwargs)
 
@@ -149,6 +148,23 @@ class GaussianProcessClassificationHead(tf.test.TestCase,
       self.assertIsInstance(outputs, tf.Tensor)
       self.assertEqual(outputs.shape, (batch_size, num_classes))
 
+  def test_sngp_train_logits(self):
+    """Checks if temperature scaling is disabled during training."""
+    features = tf.zeros(shape=(5, 10, 10), dtype=tf.float32)
+
+    gp_layer = cls_head.GaussianProcessClassificationHead(
+        inner_dim=5, num_classes=2)
+
+    # Without temperature.
+    gp_layer.temperature = None
+    outputs_no_temp = gp_layer(features, training=True)
+
+    # With temperature.
+    gp_layer.temperature = 10.
+    outputs_with_temp = gp_layer(features, training=True)
+
+    self.assertAllEqual(outputs_no_temp, outputs_with_temp)
+
   def test_layer_serialization(self):
     layer = cls_head.GaussianProcessClassificationHead(
         inner_dim=5,

official/nlp/modeling/layers/gaussian_process.py

@@ -62,7 +62,7 @@ class RandomFeatureGaussianProcess(tf.keras.layers.Layer):
                gp_kernel_scale_trainable=False,
                gp_output_bias_trainable=False,
                gp_cov_momentum=0.999,
-               gp_cov_ridge_penalty=1e-6,
+               gp_cov_ridge_penalty=1.,
                scale_random_features=True,
                use_custom_random_features=True,
                custom_random_features_initializer=None,
@@ -292,7 +292,7 @@ class LaplaceRandomFeatureCovariance(tf.keras.layers.Layer):
 
   def __init__(self,
                momentum=0.999,
-               ridge_penalty=1e-6,
+               ridge_penalty=1.,
                likelihood='gaussian',
                dtype=None,
                name='laplace_covariance'):