code: def linear_dataset(a=2, size=1000):
      x = np.random.rand(size)
      y = x / 2
  
      x = x.reshape((-1, 1))
      y = y.reshape((-1, 1))
  
      return x, y
  
imports: import math
  import os
  import shutil
  import tempfile
  import pytest
  from unittest import TestCase
  import tensorflow
  import numpy
  from bigdl.orca.data.pandas import read_csv
  from bigdl.orca.data import SparkXShards, XShards
  from bigdl.orca.data.tf.data import Dataset
  from bigdl.orca.learn.tf2 import Estimator
  from bigdl.orca.ray import OrcaRayContext
  from bigdl.orca import OrcaContext
label_desc: Use image node_id 1 for calling a global function with example usage: linear_dataset(a, size) and returns: x,  y