Comment #19 on issue 2106 by mipavelka: Matrix of shape (1,1) and a number
can't be added
http://code.google.com/p/sympy/issues/detail?id=2106
reply to comment 14:
You can also put it differently:
If 1x1 matrices were the same as scalars, it would make sense.
I think that you mean that the matrix multiplication would not make sense
and I agree. But it depeds how the * operator is defined.
It would make sense to define the A*B operation (where A and B are Matrix
instances) as
"If dimensions of neighbouring indeces of A and B match, do the dot
product. Tensor product otherwise."
I think that the * would not be defined precisely otherwise.
It also works in SymPy like that:
(1) (1 1 1) (1) (1) (1 1)
(1) * (1 1 1) = (1 1 1) but (1 1 1) * (1) = (3) or (1) * (1 1) = (1 1)
(1) (1 1 1) (1) (1) (1 1)
Then, if the SymPy * operator should have such behavior it should return
the dot product in the case row vector * column vector, i.e. a scalar. But
it gives a 1x1 matrix as a result of matrix multiplication.
I think that it would be nice to have 1x1 matrices compatible with scalars.
At least the + and * operators could be able to handle 1x1 matrix <->
scalar conversion implicitely.
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