I want to multiply A(2, 6) with B(6, 1) to obtain a Matrix with shape (2, 1).

If I use `A= ti.Matrix(1, dt=ti.f32, shape=(2, 6), needs_grad=True)`

. It will initialize a Matrix with shape (2, 6, 1, 1).

If I use `A = ti.Matrix(2, 6, dt=ti.f32, shape=1, needs_grad=True)`

. It will initialize a Matrix with shape (1, 2, 6).

I want to ask which two dimensions are multiplied when I implement multiplication another matrix.

I also want to ask which is the correct way to initialize a Matrix.

# Which dimensions of Matrix are multiplied?

I’m working on a documentation page to clarify this. Please expect that to be online in 45 minutes.

A quick answer for now:

`A = ti.Matrix(1, 4, dt=ti.f32, shape=(2, 6), needs_grad=True)`

allocates a *2x6 tensor* of *1x4* matrices. You need to first get the matrix by tensor indexing, e.g. `A[1, 5]`

, and then do your matrice multiplication using the `@`

operator.

It seems to me that the correct way for your case is to use

`A = ti.Matrix(2, 6, dt=ti.f32, shape=(), needs_grad=True)`

, which allocates you a 0D tensor of 2x6 matrices.

Thank you so much! The documents are very clear now.

Is there a way to create a matrix with dynamic shape? Like a universal data holder?

Do you mean something like `std::vector<Matrix>`

?

In C++, yes. In python, a standard torch tensor may have dynamic batch size.

Also, another question is how to pass `data = torch.zeros((2, 6))`

to `ti_data_holder = ti.Matrix(2, 6, dt=ti.f32, shape=(), needs_grad=True)`

. It says `list index out of range`

.

Sorry v0.2.4 does not support from/to_torch for 0D tensors yet. I just now pushed v0.2.5 with this feature. It will be available in 20 minutes. Example:

For something like `std::vector<Matrix>`

, see here: https://github.com/yuanming-hu/taichi/blob/4c12a6b7c6a488478ca620aa5d7f40272eaf0a0b/tests/python/test_dynamic.py#L56

Although a dynamic batch size is doable, that would require a deeper understanding into Taichi. I would suggest using a fixed batch size for now.