code: def ref_inv(x):
      y = np.zeros_like(x, dtype=np.float32)
      for i in range(x.shape[0]):
          y[i] = np.linalg.inv(x[i])
      return y
  
file_path: nnabla/python/test/function/test_batch_inv.py
imports: import pytest
  import numpy
  import nnabla
  import nnabla.functions
  from nbla_test_utils import list_context
label_desc: Use image node_id 1 for calling a global function with example usage: ref_inv(x) and returns: y