What is the type of your vector x? If it is a Matrix, this is just the
way that SymPy works. It represents "vectors" as a 1 x n matrix. If it
is an object from the sympy.vector module then I'm not sure.
I would recommend not using NumPy to manipulate SymPy objects like
that. NumPy should only be used for numeric values and ideally you
should only do so after converting your SymPy expression to a NumPy
function with lambdify(). You lose out on the benefits of using SymPy
if you store SymPy objects in a NumPy array. See
https://docs.sympy.org/dev/explanation/best-practices.html#separate-symbolic-and-numeric-code
Aaron Meurer
On Wed, Nov 1, 2023 at 8:15 PM Lenni Lemoy wrote:
>
> Hi everybody,
>
> I just started using SymPy, and tried to multiply a matrix M by a vector x
> holding sympy.symbols.
>
> I expected that M*x will be a vector again, but it is a matrix holding
> elements M_i,j*x_j.
>
> Is that the intended behavior or am I doing something wrong? I looked for
> another method I could use but found nothing adequate. Currently, I use
> np.sum(M*x, axis=1) to obtain the vector result, but this seems a little
> awkward.
>
> Thanks already for any info on this! :)
>
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