Talk:Stiffness matrix

Example
The "example" on this page is just a random matrix with no explanation at all. It should be explained with further diagrams, or deleted. Napalm Llama (talk) 15:48, 12 October 2009 (UTC)

article rewrite
I have rewritten this article to add more information and have a clearer exposition; the old version was a bit of a hodge-podge. Compsonheir (talk) 03:22, 13 August 2012 (UTC)

Could use a simpler example first
like the one with a linear arrangement of springs and masses used in Strang's Introduction to Applied Mathematics. 86.127.138.234 (talk) 03:19, 22 February 2015 (UTC)

Yes !!! The present article explains the maths of stiffness matrices to those who already have higher maths - it is not at all accessible to most Wikipedia readers with a good general education - please can someone re-write it.

Stiffness matrix for other problems
The equation should describe a relation between the solution variable $$u$$ and the right-hand side $$f$$. In the form after an edit made earlier,


 * $$ -\sum_{k,l}\frac{\partial}{\partial x_k}\left(a^{kl}\frac{\partial u}{\partial x_l}\right)\frac{\partial}{\partial x_l} = f$$

The left-hand side is a differential operator, while the right-hand side is a function. There is no way they can be equal to each other. Also, the original edit comment doesn't make sense. There is already a differential operator $$\frac{\partial}{\partial x_l}$$ in the $$\frac{\partial u}{\partial x_l}$$ part. There is no reason why $$\partial x_l$$ should appear twice. Therefore, I am reverting a previous edit to restore it to the correct form before that edit. -- 61.18.56.229 (talk) 09:47, 7 September 2021 (UTC)

Please also note that in the special case $$a^{kl}=\delta_{kl}$$, $$ -\sum_{k,l}\frac{\partial}{\partial x_k}\left(a^{kl}\frac{\partial u}{\partial x_l}\right)$$ is simply $$-\nabla^2 u$$ in the first section of this article. -- 61.18.56.229 (talk) 09:54, 7 September 2021 (UTC)