[GitHub] [singa] dcslin edited a comment on issue #639: added support for matmul 3d 4d

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dcslin edited a comment on issue #639: added support for matmul 3d 4d
URL: https://github.com/apache/singa/pull/639#issuecomment-605793210
 
 
   > is matmul different to tensordot?
   > why not call tensordot to implement it?
   
   Batch matmul could not be implemented by tensordot, as batch matmul is not really tensor dot.
   Batch matmul could be illustrated by einsum:
   ``` python
   >>> x1.shape
   (2, 3, 4, 5)
   >>> x2.shape
   (2, 3, 5, 6)
   >>> np.testing.assert_almost_equal(np.matmul(x1,x2), np.einsum('ijkl,ijlm->ijkm',x1,x2))
   # output is (2,3,4,6)
   ```
   
   
   Boardcasting matmul could be implemented by tensordot:
   ```
   >>> x1.shape
   (2, 3, 4, 5)
   >>> x3.shape
   (5, 6)
   >>> np.testing.assert_almost_equal(np.matmul(x1,x3), np.tensordot(x1,x3,axes=([3],[0])))
   # output is (2,3,4,6)
   ```

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