ctc_cost.py 文件源码

def sequence_log_likelihood(y, y_hat, y_mask, y_hat_mask, blank_symbol):
    """
    Based on code from Shawn Tan.
    Credits to Kyle Kastner as well.
    """
    y_hat_mask_len = tensor.sum(y_hat_mask, axis=0, dtype='int32')
    y_mask_len = tensor.sum(y_mask, axis=0, dtype='int32')
    log_probabs = _log_path_probabs(
        y, T.log(y_hat), y_mask, y_hat_mask, blank_symbol)
    batch_size = log_probabs.shape[1]
    log_labels_probab = _log_add(
        log_probabs[y_hat_mask_len - 1,
                    tensor.arange(batch_size),
                    y_mask_len - 1],
        log_probabs[y_hat_mask_len - 1,
                    tensor.arange(batch_size),
                    y_mask_len - 2])
    return log_labels_probab