code: def test_sgd_const_lr(self, dev=cpu_dev):
      cpu_dev.EnableGraph(False)
      sgd1 = opt.SGD(lr=0.1)
      w_shape = (2, 3)
      w = tensor.Tensor(w_shape, device=dev).set_value(0.1)
      g = tensor.Tensor(w_shape, device=dev).set_value(0.1)
  
      w_step1 = w - 0.1 * g
      sgd1.apply(w.name, w, g)
  
      assertTensorEqual(w, w_step1)
  
imports: from __future__ import division
  import math
  import unittest
  import numpy
  import functools
  from singa import tensor
  from singa import singa_wrap
  from singa import opt
  from cuda_helper import gpu_dev, cpu_dev
label_desc: Use image node_id 2 for calling the TestOptimizer obj's underlying member method code with example usage: obj.test_sgd_const_lr(dev) without return types