How to use the @tensorflow/tfjs-node-gpu.expandDims function in @tensorflow/tfjs-node-gpu

optimizer: tf.train.adam(args.learningRate, args.adamBeta1),
    loss: ['binaryCrossentropy', 'sparseCategoricalCrossentropy']
  });
  discriminator.summary();

  // Build the generator.
  const generator = buildGenerator(args.latentSize);
  generator.summary();

  const optimizer = tf.train.adam(args.learningRate, args.adamBeta1);
  const combined = buildCombinedModel(
      args.latentSize, generator, discriminator, optimizer);

  await data.loadData();
  let {images: xTrain, labels: yTrain} = data.getTrainData();
  yTrain = tf.expandDims(yTrain.argMax(-1), -1);

  // Save the generator model once before starting the training.
  await generator.save(saveURL);

  let numTensors;
  let logWriter;
  if (args.logDir) {
    console.log(`Logging to tensorboard at logdir: ${args.logDir}`);
    logWriter = tf.node.summaryFileWriter(args.logDir);
  }

  let step = 0;
  for (let epoch = 0; epoch < args.epochs; ++epoch) {
    // Write some metadata to disk at the beginning of every epoch.
    fs.writeFileSync(
        metadataPath,