if "out" = "None".
Returns:
      if the i^{th} tensor was of dimensions p_{i} \times p_{i + 1},
      then the product would be of dimensions p_{1} \times p_{N + 1}.
Return type:
      Tensor
Example:
  >>> a = torch.randn(3, 4)
  >>> b = torch.randn(4, 5)
  >>> c = torch.randn(5, 6)
  >>> d = torch.randn(6, 7)
  >>> # will raise a deprecation warning
  >>> torch.chain_matmul(a, b, c, d)
  tensor([[ -2.3375,  -3.9790,  -4.1119,  -6.6577,   9.5609, -11.5095,  -3.2614],
          [ 21.4038,   3.3378,  -8.4982,  -5.2457, -10.2561,  -2.4684,   2.7163],
          [ -0.9647,  -5.8917,  -2.3213,  -5.2284,  12.8615, -12.2816,  -2.5095]])
