A short example below:
```
from mxnet import nd
batchsz = 2
W = nd.random_normal(shape=(batchsz,3,4,5))
U = nd.random_normal(shape=(batchsz,5))
Y = nd.batch_dot(W,U)
```
And in fact, doing matrix vector product will fail too
```
W = nd.random_normal(shape=(batchsz,4,5))
U = nd.random_normal(shape=(batchsz,5))
Y = nd.batch_dot(W,U)
```
Doing the following would work:
```
W = nd.random_normal(shape=(batchsz,4,5))
U = nd.random_normal(shape=(batchsz,5,1))
Y = nd.batch_dot(W,U)
```
There really shouldn't be any reason why this only handles matrix matrix
multiplication in batch but not that of tensors and vectors.
------------------------------
Error message:
```
---------------------------------------------------------------------------
MXNetError Traceback (most recent call last)
<ipython-input-7-654c124195f4> in <module>()
3 W = nd.random_normal(shape=(batchsz,3,4,5))
4 U = nd.random_normal(shape=(batchsz,5))
----> 5 Y = nd.batch_dot(W,U)
/usr/local/lib/python3.6/site-packages/mxnet/ndarray/register.py in
batch_dot(lhs, rhs, transpose_a, transpose_b, out, name, **kwargs)
/usr/local/lib/python3.6/site-packages/mxnet/_ctypes/ndarray.py in
_imperative_invoke(handle, ndargs, keys, vals, out)
90 c_str_array(keys),
91 c_str_array([str(s) for s in vals]),
---> 92 ctypes.byref(out_stypes)))
93
94 if original_output is not None:
/usr/local/lib/python3.6/site-packages/mxnet/base.py in check_call(ret)
147 """
148 if ret != 0:
--> 149 raise MXNetError(py_str(_LIB.MXGetLastError()))
150
151
MXNetError: [00:15:08] src/operator/tensor/./dot-inl.h:1265: batch_dot
currently only support 3D*3D array[2,3,4,5] v.s. [2,5]
Stack trace returned 9 entries:
[bt] (0) 0 libmxnet.so 0x000000010e4494b4 libmxnet.so
+ 21684
[bt] (1) 1 libmxnet.so 0x000000010e44926f libmxnet.so
+ 21103
[bt] (2) 2 libmxnet.so 0x000000010e448ee9 libmxnet.so
+ 20201
[bt] (3) 3 libmxnet.so 0x000000010e90f7db libmxnet.so
+ 5027803
[bt] (4) 4 libmxnet.so 0x000000010f5547fa
MXNDListFree + 431770
[bt] (5) 5 libmxnet.so 0x000000010f553459
MXNDListFree + 426745
[bt] (6) 6 libmxnet.so 0x000000010f4c478a
MXCustomFunctionRecord + 20250
[bt] (7) 7 libmxnet.so 0x000000010f4c5990
MXImperativeInvokeEx + 176
[bt] (8) 8 _ctypes.cpython-36m-darwin.so 0x000000010d39f427
ffi_call_unix64 + 79
```
[ Full content available at:
https://github.com/apache/incubator-mxnet/issues/12307 ]
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