How to construct a symmetric matrix in nalgebra?

[hunter1992]

My goal is to construct a symmetric matrix M, which is composed of some known submatrices.

For example, the M I'm gonna construct is

$$ M=\begin{bmatrix} M_{11}&M_{12}\\ M_{21}&M_{22}\\ \end{bmatrix} $$

And the submatrix $M_{ij}$ are some known submatrices:

$$ M_{11} = \begin{bmatrix} a&b\\ b&a\\ \end{bmatrix} $$

$$ M_{12} = \begin{bmatrix} c&d\\ e&f\\ \end{bmatrix} $$

$$ M_{21} = \begin{bmatrix} c&e\\ d&f\\ \end{bmatrix} $$

$$ M_{22} = \begin{bmatrix} g&h\\ h&i\\ \end{bmatrix} $$

That is to say, the final M matrix is:

$$ M= \begin{bmatrix} a&b&c&d\\ b&a&e&f\\ c&e&g&h\\ d&f&h&i\\ \end{bmatrix} $$

I want to know if there is a method in nalgebra that can still efficiently construct M when the size of M is large.

In Python, the numpy has hstack or vstack function to implement my desire.
Is there a function with the same functionality in nalgebra？

[Andlon]

#1375 is ready to merge, and it'll probably make it to the next release. Hopefully this will be soon. In the meantime, you'll have to:

1. construct your output matrix with Matrix::zeros
2. use e.g. .view_mut(...) to construct a view for each block
3. populate each view with e.g. view.copy_from(&M_11)

Hopefully the new stack! macro will make this a breeze.

[Andlon]

To elaborate, since there's no example in the PR description, you'll be able to write:

let m = stack![ m11, m12;
                m21, m22 ];

[hunter1992]

@Andlon Thank you very much! :)