code: def check_backward(self, x_data, y_grad):
      def f(x):
          return distributions.multivariate_normal._triangular_inv(
              x, lower=self.lower
          )
  
      gradient_check.check_backward(
          f, x_data, y_grad, **self.backward_options
      )
  
imports: import unittest
  import numpy
  from chainer import cuda
  from chainer import distributions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 5 for calling the TestTriangularInv obj's underlying member method code with example usage: obj.check_backward(x_data, y_grad) and returns: distributions