I think this should be simple, but I'm drawing a blank

I have 2 2d matrixes

Matrix A has indexes (i, symbol)
Matrix B has indexes (state, symbol)

I combined them into a 3d matrix:

C = A[:,newaxis,:] + B[newaxis,:,:]
where C has indexes (i, state, symbol)

That works fine.

Now suppose I want to omit B (for debug), like:

C = A[:,newaxis,:]

In other words, all I want is to add a dimension into A and force it to
broadcast along that axis.  How do I do that?