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I have two matrices user_vecs and item_vecs

I am trying to take the dot product of the two to build a recommendation engine:

The shape of the two vectors are as follows:

user_vecs.shape

(20051, 20)

item_vecs.shape

(20,1808)

When i take the dot product of the transpose as follows:

a = user_vecs.dot(item_vecs.transpose())

I get the following error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-41-f4cd01978711> in <module>
----> 1 a = user_vecs.dot(item_vecs.transpose())

C:\ProgramData\Anaconda3\lib\site-packages\scipy\sparse\base.py in dot(self, other)
    362 
    363         """
--> 364         return self * other
    365 
    366     def power(self, n, dtype=None):

C:\ProgramData\Anaconda3\lib\site-packages\scipy\sparse\base.py in __mul__(self, other)
    479         if issparse(other):
    480             if self.shape[1] != other.shape[0]:
--> 481                 raise ValueError('dimension mismatch')
    482             return self._mul_sparse_matrix(other)
    483 

ValueError: dimension mismatch

i understand that the dimensions of the two matrices are not matching, but the transpose should have fixed that. Why am I still getting this error?

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Firstly user_vecs, item_vecs are matrices, not vectors, since both the shapes are of two dimensions. If seems like you are trying to multiply both the matrices, so you can simply use user_vecs.dot(item_vecs). No need to transpose item_vecs. You can also use np.matmul(user_vecs, item_vecs). Refer to this thread for more details.

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