From 0a0e07a1931f69e3801c3d235068b52f24d4d13d Mon Sep 17 00:00:00 2001
From: Zchen <161216199+ZH-CEN@users.noreply.github.com>
Date: Mon, 20 Oct 2025 01:16:50 +0800
Subject: [PATCH] Remove custom CTC loss implementation for TPU from the
 TripleGRUDecoder class

---
 model_training_nnn_tpu/rnn_model_tf.py | 67 --------------------------
 1 file changed, 67 deletions(-)

diff --git a/model_training_nnn_tpu/rnn_model_tf.py b/model_training_nnn_tpu/rnn_model_tf.py
index 6a0e7c8..42d0302 100644
--- a/model_training_nnn_tpu/rnn_model_tf.py
+++ b/model_training_nnn_tpu/rnn_model_tf.py
@@ -689,73 +689,6 @@ class TripleGRUDecoder(keras.Model):
         self.training_mode = mode
 
 
-# Custom CTC Loss for TensorFlow TPU
-class CTCLoss(keras.losses.Loss):
-    """
-    Custom CTC Loss optimized for TPU v5e-8
-    """
-
-    def __init__(self, blank_index=0, reduction='none', **kwargs):
-        super(CTCLoss, self).__init__(reduction=reduction, **kwargs)
-        self.blank_index = blank_index
-
-    def call(self, y_true, y_pred):
-        """
-        Args:
-            y_true: Dictionary containing 'labels', 'input_lengths', 'label_lengths'
-            y_pred: Logits tensor [batch_size, time_steps, num_classes]
-        """
-        labels = y_true['labels']
-        input_lengths = y_true['input_lengths']
-        label_lengths = y_true['label_lengths']
-
-        # Ensure correct data types
-        labels = tf.cast(labels, tf.int32)
-        input_lengths = tf.cast(input_lengths, tf.int32)
-        label_lengths = tf.cast(label_lengths, tf.int32)
-
-        # Convert logits to log probabilities
-        log_probs = tf.nn.log_softmax(y_pred, axis=-1)
-
-        # Transpose for CTC: [time_steps, batch_size, num_classes]
-        log_probs = tf.transpose(log_probs, [1, 0, 2])
-
-        # Convert dense labels to sparse format for CTC using TensorFlow operations
-        def dense_to_sparse(dense_tensor, sequence_lengths):
-            """Convert dense tensor to sparse tensor for CTC"""
-            batch_size = tf.shape(dense_tensor)[0]
-            max_len = tf.shape(dense_tensor)[1]
-
-            # Create mask for non-zero elements
-            mask = tf.not_equal(dense_tensor, 0)
-
-            # Get indices of non-zero elements
-            indices = tf.where(mask)
-
-            # Get values at those indices
-            values = tf.gather_nd(dense_tensor, indices)
-
-            # Create sparse tensor
-            dense_shape = tf.cast([batch_size, max_len], tf.int64)
-
-            return tf.SparseTensor(indices=indices, values=values, dense_shape=dense_shape)
-
-        # Convert labels to sparse format
-        sparse_labels = dense_to_sparse(labels, label_lengths)
-
-        # Compute CTC loss
-        loss = tf.nn.ctc_loss(
-            labels=sparse_labels,
-            logits=log_probs,
-            label_length=None,  # Not needed for sparse format
-            logit_length=input_lengths,
-            blank_index=self.blank_index,
-            logits_time_major=True
-        )
-
-        return loss
-
-
 # TPU Strategy Helper Functions
 def create_tpu_strategy():
     """Create TPU strategy for distributed training on TPU v5e-8"""