Talk:Minimal subtraction scheme

Toy example

I have added what I believe to be a correct abstract of the material at Butcher group as an accessible "toy" example. A.K.Nole (talk) 17:42, 30 June 2009 (UTC)

You don't have the slightest clue what you are writing and I suppose soon will receive a fairly lengthy block. Mathsci (talk) 19:45, 30 June 2009 (UTC)

Discussion of disputed material

I attempted to add the following text as new section "Example":

An example of the minimal subtraction scheme may be found in the formalism associated to the Butcher group, where the Feynman rules are given by a homomorphism taking values in the algebra V of Laurent series in z with poles of finite order and the renormalization scheme is given by a linear operator R on V such that R satisfies the Rota-Baxter identity $R(fg)+R(f)R(g)=R(fR(g))+R(R(f)g)$ and the image of R – id lies in the algebra V₊ of power series in z.

In this context the minimal subtraction scheme may be expressed as taking the principal part

$\displaystyle R(\sum _{n}a_{n}z^{n})=\sum _{n<0}a_{n}z^{n}.$

User Mathsci objected on various grounds [1], of which I extract the relevant sections here:

• you copied and pasted material from one article into another. The problem with this edit is that it is not relevant to the stub and the material is completely out of context in this article. You are unwittingly using the notation of Hopf algebras but don't seem to have a clue that you're doing so.
• Why are you adding unsourced material and unexplained notation to an article? The normal way is to find the material in a book, e.g. Collins' Renormalization, paraphrase it and then cite it.
• why did you paste material on renormalization in the toy case of rooted trees rather than the usual setting of Feynman diagrams? That was a very ill-advised error

These are very reasonable questions which I propose to address here. A.K.Nole (talk) 19:48, 30 June 2009 (UTC)

• Copy-and-paste is not in itself a bad thing. However. In this particular case I selected a small amount of material from a long, detailed and very expert article (largely written by Mathsci). The homomorphisms in question are indeed Hopf algebra homomorphisms but this is not relevant, and i removed that phrase, since the renormalisation rule applies entirely to the image space V. I added the comment that renormalisation is the principal part operation.
• It is adequately sourced in Butcher group: detailed references welcome. The notation is entirely contained in the selected text, where the operator R and space V are adequately explained.
• It is indeed a toy case, and the suggestion that this should be made clear is a good one. Its value to the non-expert is precisely that, as a toy, it is an example giving a flavour of the scheme in terms of mathematical concepts at a level that could be understood by an undergraduate. Another reason for its selection is that this is, so far, the only example of an MSS currently present in Wikipedia.

I trust that explains everything and that there is now consensus to restore the section. A.K.Nole (talk) 20:01, 30 June 2009 (UTC)

Yes there is nine months later. 134.50.3.202 (talk) 01:18, 16 December 2009 (UTC)