Talk:Elliptic curve
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The formulas would be correct if the Weierstrass form y^2=4x^3 + bx + c, was unique, but it is not. For instance if we take the lattice Z[i], the lambda value is -1. The formula in the article gives values for g2,g3 which give a cubic polynomial that should cut out the correct Riemann surface. But the particular cubic is not the one coming from the differential equation satisfied by \wp, and g2,g3 should be the coefficients for that cubic. (In the Z[i] example, the g2 value appears to be transcendental, while the articles in the formula give algebraic numbers.) Perhaps someone more experienced with wiki editing could fix this?
A quick note : I find the animating demonstration of associativity to be fascinating.. but it seems to me the labels of the points are incorrect? The 'zero' is fixed (good), but then, for example 'a' + 'b' should be further from the origin than 'a' or 'b' alone? Can some kind wiki-helper get in touch with the .GIF author and double check everything is in order? — Preceding unsigned comment added by 210.55.212.205 (talk) 20:54, 16 December 2014 (UTC)[reply]
Never mind - I re-read the article, and all seems correct now! My bad :D — Preceding unsigned comment added by 210.55.212.210 (talk) 21:51, 16 December 2014 (UTC)[reply]
I'm confused here. In the text, it states:
But, for example, the x-axis intersects the curve y2 = x3 - x + 1 at only 1 point (call it P); if we consider the other two points as being infinity, this seems to require that P + inf + inf = 0. However, the x-axis is not alone in this property; several lines parallel to the x-axis also intersect at only 1 point, if we select one of these and call the point of intersection Q, then Q + inf + inf = P + inf + inf = 0 implies P = Q. Bzzzt!!!! Is the group operation restricted to those lines which actually intersect at at least two points (where tangency counts as 2 points)? Chas zzz brown 02:00 Jan 22, 2003 (UTC)
My statement above was wrong: it only that way only for algebraically closed base fields. You're right: if the fields isn't algebraically closed, we only consider lines that are tangent to the curve or intersect it in two points. AxelBoldt 17:23 Jan 22, 2003 (UTC)
I'd like to see a bit more about the group aspect of elliptic curves over finite fields (with an eye towards ECC); especially more describing an algebraic (as opposed to geometric) approach to calculating P + Q (see [1] for a nice explanation). Should that be done at this article, at the article for elliptic curve cryptography, or at a new article? Chas zzz brown 20:04 Feb 7, 2003 (UTC)
I think it can still fit here. Can't we give the general group law formula which works for all base fields? AxelBoldt 07:37 Feb 9, 2003 (UTC)
Added the restriction that K not have characteristic 3 - observe that in the diagrams in the article, there is a point P with the property P + P + P = 3P = 0 (in the y2 = x3 - x - 1 example, it's the intersection of the y-axis and the curve). Chas zzz brown 19:57 Feb 12, 2003 (UTC)
Page needs sections now. Charles Matthews 09:51, 21 Mar 2005 (UTC)
—Sean κ. + 23:33, 27 May 2005 (UTC)[reply]
Would be nice to have graphs of singular weierstrass equations, illustrating both cusps and intersections.
On this point, it would also be nice to mention that the group law can still be defined for a singular curve, as long as we leave out the singular point (of which there can only be one -- I think). Dmharvey 17:00, 30 May 2005 (UTC)[reply]
The article describes elliptic curves as being of the form . However, in Dan Bernstein's Elliptic Curve Diffie Hellman library, he uses the curve where . Is this still an elliptic curve?
Does anyone know why these curves are called elliptic curves? My apologies if I missed it in the article. -Monguin61 01:47, 10 December 2005 (UTC)[reply]
The article covers four cases for adding points, but it leaves out the case P+P where P is a point of inflection of the curve such that the line is horizontal or otherwise fails to intersect the curve at a third finite point. I don't want to edit the article because I'm far from an expert on this topic, but this is a fundamentally different case, is it not? --24.15.231.4 04:56, 16 December 2005 (UTC)[reply]
In the article they cite 'second pane' for case 'yP = yQ' whereas in pane 2 it is obviously not the case, seems to me ?Cédric VAN ROMPAY (talk) 14:44, 12 November 2013 (UTC)[reply]
In the article: "If xP = xQ, then there are two options." But in my opinion there is also the option P=O or Q=O (O being the point at infinity). — Preceding unsigned comment added by Madyno (talk • contribs) 13:09, 29 November 2021 (UTC)[reply]
What do we call those?I've heard them being called Elliptic curves.Or non-singular curves on this form
y^2 z + axyz + byz^2 = x^3 + cx^2 z + d x z^2 + e z^3
being called elliptic curves...
Your definition appears to be different.
Can someone with knowledge disambig varieties in the Isogeny section? Thanks. Simon12 02:26, 1 July 2006 (UTC)[reply]
"By adding a "point at infinity", we obtain the projective version of this curve"
why one point? by Bezout theorem, this curve has exactly 3 points at infinity. 84.108.112.10 12:50, 14 April 2007 (UTC)[reply]
Doesn't this statement depend on the embadding of the elliptic curve? Liransh 19:54, 3 May 2007 (UTC)[reply]
Stca74 12:53, 26 May 2007 (UTC)[reply]
I am an arithmetic geometer working in the field(s?) of elliptic curves and curves of genus one. Here are my reactions to the article as currently written (it is quite good overall):
The basic definition -- "an elliptic curve is..." is close but needs even more care: first of all, if one is going to define it in earnest using the language of algebraic / arithmetic geometry (BTW, it is not clear to me that one should do this right away; more people would understand the y^2 = x^3+ax+b definition, which is not wrong, just overly concrete for some purposes), you are missing the proviso "geometrically connected." More seriously, you are missing a mention of the field of definition of the elliptic curve. As stated above, for about 100 years it has been the case that elliptic curves are interesting only over non-algebraically closed fields, so the dependence on the field should be made clear from the start. Again, a reasonable choice would be to say a bit first about elliptic curves over the rational field and then start again with a definition over an arbitrary field (with the longer Weierstrass equation).
Nitpicking point: the definition of an elliptic curve in short Weierstrass form is not insufficiently "precise"; it is simply not the definition of an elliptic curve in char. 2 or 3 that agrees with the above geometric definition (i.e., the problem is not precision; it's simply a matter of a statement which is no longer true).
The paragraph beginning "If y^2 = P(x)..." is a bit awkwardly written. In particular, somewhere in this paragraph the fact that an elliptic curve must have a rational point is forgotten. The point of the Weierstrass form is that it comes equipped with a canonical rational point (the inflection point at infinity). The other forms -- hyperelliptic quartic, plane cubic and intersection of two space quadrics -- are important alternate ways of presenting smooth curves of genus one, but in these other forms a rational point is not guaranteed (rather, a rational divisor of degree 2, 3, or 4, respectively).
Saying that the proof of FLT is by Wiles assisted by Taylor is not ideal -- the work of Taylor and Wiles was indeed spectacular, but it also built on important work of many other mathematicians: e.g. Ribet, who proved that Taniyama-Shimura implies FLT. The attribution of FLT is a complicated story which can be left to the article itself; no need to try to wing it here.
"By adding a 'point at infinity', we obtain the projective version of this curve" This could be better phrased. The projectivization of an affine curve is an easy general construction: we just homogenize the defining polynomial by inserting in each monomial term whatever power of Z brings the total degree of each term up to the maximum of the total degrees of the original terms (in this case 3, of course). Surely this is described somewhere onsite? (If not, it should be!) Then the fact that the line at infinity intersects a Weierstrass cubic in a single point can be verified. My point is that the way it is said it sounds like one knew in advance that there was one point to add. This is really not the case, since e.g. one could work with a non-Weierstrass cubic endowed with a rational point, and then the projectivization could add as many as three points.
In your definition of the group law: you never actually say what P+Q _is_, you just give defining properties. Why not say that if R is the third intersection point of P and Q with the curve, then P+Q is the third intersection point of O and R with the curve (and illustrate this with a picture)?
"One can check that this turns the curve into an abelian group, and thus into an abelian variety." Bad -- an abelian variety is a commutative group variety but not conversely (think of the additive group or the multiplicative group, e.g.). The sentence could read, "One can check that the K-rational points on E form an abelian group under +. [insert some indication that the associativity is the sticky point!] Moreover, as a map from E x E to E, the addition law is "algebraic", i.e., given by rational functions on E, so endows E with the structure of an algebraic group (and indeed, since E is projective and geometrically connected, an abelian variety." Or you could not say all these things -- it's not really necessary.
"The above group law can be described algebraically as well as geometrically." I object to this dichotomy here and elsewhere in the article: the above description of the group law is both algebraic _and_ geometric (and also arithmetic, since it takes fields of rationality into account). It is not necessary to perform the construction first over the real numbers and then describe it separately -- it makes sense over any field using simple, purely algebraic definitions of partial derivative, tangent line, etc. "Algebraically" and "using the following explicit equations" are not synonymous!
Elliptic curves over the complex numbers: "curious property of Weierstrass's elliptic functions..." "Curious" is unencyclopedic. Anyway, it is not explained. "Looks like" |-> "is homeomorphic to" (with a link). The reader who has made it this far will not be confused. ... "then the corresponding elliptic curves are isomorphic" And conversely!
"The isomorphism classes can be understood in a simpler way..." "Simpler" is POV.
"The complex numbers are the splitting field for polynomials" -> "the complex numbers are algebraically closed"
Drop the name "Legendre form" for the y^2 = x(x-1)(x-lambda) and give a reference (say, to Silverman) for all these formulas.
"The uniformization theorem states" |-> "The uniformization theorem implies." (It says other things as well.)
Elliptic curves over a general field: again, I wish this would be more gracefully incorporated into the above. (One way to do it is to do it over Q in a way that works over an arbitrary field, and then later to announce this.)
"One typically takes the curve to be..." This is not quite right; a curve is a curve, in the sense of arithmetic geometry. It is not simply the set of its points over the algebraic closure (although the set of points together with all morphisms from it are sufficient to recover the algebraic structure). It is better not to say anything about this subtle point than to get it a little bit wrong.
Isogeny of elliptic curve: the term "basepoint" (should be "base point") has not been used above. (Better, e.g. "the origin", or "the neutral element".) About the homomorphism property of an isogeny: moreover, the homomorphism is surjective over the algebraic closure.
"no general algorithm is known..." Elaborate on this point. There is an algorithm which we use in practice, which will work provided Shafarevich-Tate groups are finite. (The point is that having an "algorithm" that has not been proved to terminate in all cases is not the same as not having any idea at all how to start computing.)
"A formula for this rank is given by..." This is true, but the other terms in the formula are difficult both theoretically and computationally as well.
"This fact can be understood and proven with the help of some general theory..." Well, okay. I wonder whether the people who are conversant (or even potentially conversant) with etale cohomology are really looking on Wikipedia to find out how to prove Hasse's bound. Of course Hasse's proof was simpler, and there is also a relatively simple proof in Silverman's book: a reference here would be nice.
"The number of points on a specific curve..." It would be hard to compute the number of points on a nonspecific curve, wouldn't it? :)
It would be nice also to have a section on elliptic curves over local fields and reduction theory, as well as a little bit about complex multiplication.
Well, I can help out with these changes, but not tonight. 128.192.134.50 06:58, 14 August 2007 (UTC)Plclark[reply]
Is it obvious to everybody but me that the elliptic-curve "addition" operation is associative? How on earth did anybody ever notice, "Hey, if I define a combination operation like this, it's associative, so I can get a group!" 68.189.88.169 (talk) 22:42, 2 March 2008 (UTC)[reply]
The article now contains a very nice animation, and purports this to provide a geometric proof of associativity. I have seen proofs of associativity with very similar diagrams (in the textbook by Niven, Zuckerman, and Montgomery, for example), but the proof includes considerably more material than currently in this wikipedia article. For example, Bezout's theorem says two cubics intersect in nine points, but one may need even more to complete the proof of associativity: such that if three cubics share eight points, then the ninth point in each of pairwise intersections is identical. Just to be clear I am only guessing that something like that would complete the proof. (By the way, in the diagram the three cubics are (1) the curve, and (2) the three nearly vertical lines and (3) the three nearly horizontal lines. The ninth point in question is the central point.) In other words, the article is now wrong: a geometric proof is not supplied. I will try to remove this claim, without hindering the importance and intuition of the animation. I hope that somebody else can supply the missing parts of the proof. DRLB (talk) 15:50, 13 May 2013 (UTC)[reply]
Sorry to bother you, but it is written "The article now contains a very nice animation" at 15:50, 13 May 2013 (UTC), but I can't find the "animation", or perhaps it stopped being animated and is just a simple picture. Please fix or explain ... (Peter10003 (talk) 16:49, 28 July 2017 (UTC))[reply]
I really like the animation, and I think it nicely illustrates the Cayley-Bacharach theorem (though not its proof). However, for the elliptic curve group law, it seems a little off, because O is not an inflection point. (True, any point can serve as O, but if O is a non-inflection points, the chord-and-tangent law does not define addition, if I recall correctly.) In the animation, O does not look like an inflection point. Not sure who knows how to modify the animation. DRLB (talk) 00:58, 31 July 2017 (UTC)[reply]
Did we lose something along the way? The O in the first sentence doesn't seem to help with the definition. Perhaps there was some characteristic of O that is missing? (John User:Jwy talk) 23:00, 19 October 2008 (UTC)[reply]
The requirement for a point O forces the curve to have a rational projective point. Curves without any rational projective points are not elliptic curves. In practice, most of the time, the curve is chosen to have a single point at infinity which is taken for O, but this is not a requirement.83.159.7.181 (talk) 10:13, 17 July 2012 (UTC)[reply]
I'm not an algebraic geometer/number theorist, but this looks wrong: "For prime numbers ℓ not dividing N, the coefficient \scriptstyle a(\ell) of the form equals ℓ – the number of solutions of the minimal equation of the curve modulo ℓ." Shouldn't it be "...equals aℓ – the number of solutions..."? If so, probably needs a reference — Preceding unsigned comment added by 203.24.207.178 (talk) 06:10, 31 July 2012 (UTC)[reply]
why didn't you like my edit?
The link to Tunnell, as it stands, isn't useful. The referenced Tunnell isn't even one of those mentioned in the disambiguation page, whereas I proposed an useful link.
At least an explanation is in order instead of just bluntly undoing. — Preceding unsigned comment added by 89.247.124.39 (talk) 13:21, 24 December 2012 (UTC)[reply]
Original anonymous here: Oops -- I stand corrected. I can't reproduce the problem now: the new link is there. Let's assume it was my browser playing nasty caching tricks on me.
Please accept my apologies — Preceding unsigned comment added by 89.247.13.63 (talk) 10:20, 26 December 2012 (UTC)[reply]
I came here looking to remind myself how the rational points of an elliptic curve were defined, and was annoyed that halfway through the article the symbols E(Q) is introduced without explanation. For lots of people this would mean nothing. I'm enough of a mathematician that I know it means the rational points of the elliptic curve... however, the article should explain this and say exactly what the rational points are. (For example, presumably the point at infinity is a rational point.) — Preceding unsigned comment added by John Baez (talk • contribs)
Section 3 seems to contain some fundamental mistakes. The formulas linking $g_2$, $g_3$ and $\Delta$ to $\lambda$ are clearly wrong, since the former are modular forms (transforming with a non-trivial weight) and the latter a modular function (transforming without a weight). I am not sure how to fix this.129.16.128.185 (talk) 14:07, 9 June 2016 (UTC)[reply]
Under the section Elliptic curves over the complex numbers, this passage appears:
"the Weierstrass functions are naturally defined on a torus T = C/Λ. This torus may be embedded in the complex projective plane by means of the map
This map is a group isomorphism, carrying the natural group structure of the torus into the projective plane."
But it is not clear what it means to say that the map is a group isomorphism.
The projective plane does not carry a group structure of its own. So in what sense does the image of this map even have a group structure?
Of course, any bijection from a group to a set can be used to transfer the group structure of the group to one on its image. But in this case it is confusing to call that an isomorphism (even though it is one): It is just a map used to copy a group from one set onto another set.
I hope someone more knowledgeable than I will improve the exposition here.Daqu (talk) 19:07, 5 September 2016 (UTC)[reply]
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There is the following mistake in the gif:
The "minus points", e.g. -(a+b), are incorrect. The labeling is based on the misconception that "three points on a line add up to 0". This is however only true if 0 is itself an inflection point.
That it is not true otherwise can easily be seen by considering the tangent at 0 itself.
The fix is that first the "minus labels" should be deleted and then also a line from 0 trough the middle point (currently labeled -(a+b+c)) should be drawn. The third intersection is then a+b+c. — Preceding unsigned comment added by Claus from Leipzig (talk • contribs) 20:22, 21 June 2017 (UTC)[reply]
I have now deleted the incorrect gif. It would of course nice to have a correct one.Claus from Leipzig (talk) 08:11, 21 July 2017 (UTC)[reply]
I just deleted this section.Claus from Leipzig (talk) 20:13, 8 August 2017 (UTC)[reply]
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Surely the formulas for g_2 and g_3 here need to be multiplied by something. The modular lambda function :H -> C is invariant under all of \Gamma(2) but g_2 and g_3 are not, so they cannot be polynomials in \lambda.
I think for instance the formula for g_3 needs to be multipled by the modular form -4 \pi^6 \theta_3(0,1+\tau)^{12} (after replacing \lambda by 1-\lambda).
It's nicely written and I don't advocate increasing the complexity, but surely simplifying things to the point of incorrectness can't have been the best choice. Createangelos (talk) 09:56, 11 February 2019 (UTC)[reply]
Why is the coefficient of the x3 term shown as 4? Doesn't 4=1 in a field of characteristic 3?MeanStandev (talk) 18:07, 27 June 2020 (UTC)[reply]
In Elliptic curves over the rational numbers:The structure of rational points the largest known rank is ">=28". There is no mention of how it is then determined how this might become "=28". Is this worth mentioning?
Darcourse (talk) 04:50, 26 April 2022 (UTC)[reply]
The reference for the book "Algorithms for Modular Elliptic Curves" links the author to the article on the Maltese politician John Joseph Cremona (https://www.search.com.vn/wiki/en/John_Cremona). The author is in fact John E. Cremona, emeritus professor at the University of Warwick (https://warwick.ac.uk/fac/sci/maths/people/staff/john_cremona/, https://johncremona.github.io/). — Preceding unsigned comment added by Autoplunger (talk • contribs) 03:59, 13 May 2022 (UTC)[reply]
This looks nice, but detailed discussion of the proof and its implications seems like it should belong on the Mordell–Weil theorem page rather than in a subsection here. To be specific, I think the part from "The proof of the theorem involves two parts." to "The theorem however doesn't provide a method to determine any representatives of E(Q)/mE(Q)." can be moved. Kclisp (talk) 17:12, 26 March 2023 (UTC)[reply]
The introductory section contains this passage:
"The curve is required to be non-singular, which means that the curve has no cusps or self-intersections. (This is equivalent to the condition 4a3 + 27b2 ≠ 0, that is, being square-free in x.)"
1. What is it that is supposedly "square-free in x" ???
2. What does "square-free in x" mean here?
I hope that someone familiar with the subject and also familiar with writing clearly in English can fix this.