tensor types.
  * **requires_grad** (*bool**, **optional*) -- If autograd should
    record operations on the returned tensor. Default: "False".

Example:
  >>> torch.logspace(start=-10, end=10, steps=5)
  tensor([ 1.0000e-10,  1.0000e-05,  1.0000e+00,  1.0000e+05,  1.0000e+10])
  >>> torch.logspace(start=0.1, end=1.0, steps=5)
  tensor([  1.2589,   2.1135,   3.5481,   5.9566,  10.0000])
  >>> torch.logspace(start=0.1, end=1.0, steps=1)
  tensor([1.2589])
  >>> torch.logspace(start=2, end=2, steps=1, base=2)
  tensor([4.0])
