Talk:Lie algebroid

Reference to the correct type of stack

There was a wikilink in the Examples section from the word stacky to Stack (category theory), which has now been split. Based on the context, I've redirected towards Algebraic stack, which continues to have the subject matter of the old article. It seems, however, that rather than an algebraic stack the actually proper reference should be to the differential-geometric analogue of an algebraic (presumably Deligne-Mumford type) stack. However, these objects do not yet have a page. A quick reference to such objects will be added to algebraic stacks, together with a brief explanation of how they relate to various types of étendues (the topos-theoretic analogue). If the above is a misunderstanding of the context on this page and that the link should point elsewhere, please do fix it. Stca74 09:07, 10 September 2007 (UTC)

added section about associated Lie algebroid

It is certainly a quite short explanation, but is it also comprehensible for someone dealing with differential geometry? I have added an explicit example to clarify the relation between the target map and left-invariant vector fields/ functions. Should I be more explicit about this correlation?

Of course there are some proofs neglected behind the statements of identification, ... . These follow from elementary properties in differential geometry and are left to the reader.

[melli]64.178.100.37 (talk) 09:11, 24 February 2008 (UTC)

still stub?

Could someone mention further topics you wish to be added before the article is no longer considered stub? [melli] 64.178.100.37 (talk) 09:19, 24 February 2008 (UTC)

Probably, exterior differentiation and Schouten Gerstenhaber algebra associated to a Lie algebroids (actually, equivalent presentations) are needed, in my opinion (193.137.102.7 (talk) 17:38, 25 November 2008 (UTC)).

Not a stub any longer. 67.198.37.16 (talk) 21:16, 29 May 2024 (UTC)

Missed Def of the anchor map

The definition of the anchor map in the construction of the Lie algebroid of a Lie groupoid is missing.

Definition of morphism must be included, too. — Preceding unsigned comment added by 92.226.55.226 (talk) 10:43, 11 November 2011 (UTC)

This all seems to be in place, now. 67.198.37.16 (talk) 21:26, 29 May 2024 (UTC)

Help with example

Does anyone know how to figure out the anchor map for the example I wrote up? — Preceding unsigned comment added by Username6330 (talk • contribs) 22:27, 10 November 2017 (UTC)

Unspecified symbol

I think one should define the dot product in the first equation.217.234.135.12 (talk) 14:18, 3 October 2018 (UTC)

Excellent question. From context, it is some bundle metric. It's deeply disconcerting that this is not spelled out explicitly, since, it seems to me that there's a lot of room for fiddle-faddle just right there. I left a message for User:Francesco Cattafi, who is the reigning expert on this topic, based on edit history. 67.198.37.16 (talk) 20:50, 29 May 2024 (UTC)

Oh, effing a. $\rho (X)f$ is just a friggin scalar, so this is just a simple scalar product. Dohhh! Updating article now. 67.198.37.16 (talk) 21:19, 29 May 2024 (UTC)

Thank you for pointing it out, the formula was indeed ambiguous. As you figured out, no bundle metric is needed; however, just saying "scalar product" is still not completely precise: $\rho (X)f\cdot Y$ is actually the (pointwise) product between the smooth function $\rho (X)f$ and the vector field $Y$, so it would be not the standard "scalar product" of a vector space over the field of real numbers, rather that of a module over the ring $C^{\infty }(M)$. Or course, when applying everything to a point $x\in M$, one has the classical scalar product between a real number and a vector. I therefore did a minor rephrasing of your update (also to make the previous sentence even clearer). Francesco Cattafi (talk) 13:21, 29 June 2024 (UTC)

Notation for vector bundle

In relation to he question above, this article currently writes that $A\to M$ is a vector bundle, rather than the more conventional $\pi :A\to M$. This is a really minor point, but would help with clarity overall. I'm not making this change, if only because I don't know what notation the Lie algebroid community prefers for this. 67.198.37.16 (talk) 21:14, 29 May 2024 (UTC)

Yes, you are right that, when denoting a vector bundle, one should technically give not only the name of the total and the base space, but also of the projection.

However, it is indeed very standard to denote Lie algebroids just as $A\to M$, and write explicitly the $\pi$ only if the name for such map is needed in some formula later on. I would say that this habit is very common not only in the Lie algebroid community, but in any field in differential geometry which use vector bundles routinely. I see it a bit like using the notation $G$ for a group instead of the more complete and formally correct notation $(G,\cdot )$ or $(G,m)$.

The general (even if apparently paradoxically) principle behind these habits is to prevent an inflation of (unnecessary) symbols, for the sake of a better clarity. Of course this does not hold for more basic introductions to the topics, and indeed the pages Vector bundle and Group, for instance, use the "complete notation", but in more advanced pages, such as this one on Lie algebroids (or e.g. Connection (vector bundle)), I deem it not necessary. Francesco Cattafi (talk) 13:43, 29 June 2024 (UTC)