"torch.complex128".
Example:
  >>> import numpy as np
  >>> abs = torch.tensor([1, 2], dtype=torch.float64)
  >>> angle = torch.tensor([np.pi / 2, 5 * np.pi / 4], dtype=torch.float64)
  >>> z = torch.polar(abs, angle)
  >>> z
  tensor([(0.0000+1.0000j), (-1.4142-1.4142j)], dtype=torch.complex128)
