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Elliptic curve

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An elliptic curve is a specific type of smooth, projective, algebraic curve. In mathematics, it is defined as a curve with a genus of one. To be considered an elliptic curve, the shape must also have a specified point known as the identity element.

ECClines
ECClines

These curves are defined over a field, which describes the points within a Cartesian product. For most fields, where the characteristic is not 2 or 3, the curve can be expressed as a plane algebraic curve. This curve consists of the solutions to a specific equation. This equation describes how the points on the curve relate to one another mathematically.

A crucial requirement for an elliptic curve is that it must be non-singular. Non-singular means the curve is smooth and lacks any cusps or self-intersections.

ECClines-3
ECClines-3

Algebraically, this condition is met if the discriminant of the equation is not zero. If the discriminant is zero, the curve might have a sharp point or cross itself, which would disqualify it. For real numbers, the shape of the graph depends on this discriminant. If the discriminant is positive, the real graph has two separate components. If the discriminant is negative, the graph has only one component.

One of the most important features of an elliptic curve is its group law. An elliptic curve is an abelian variety, meaning it has a group law defined algebraically. This law allows us to perform addition on the points of the curve. The identity element for this group is the marked point, often located at infinity.

ECClines
ECClines

To add two points, P and Q, you first draw a straight line through them. This line will intersect the cubic curve at a third point, which we can call R. To find the sum, you then take the point opposite to R. This geometric method is known as the tangent and secant method. If you only have one point, you use the tangent line at that specific spot.

Elliptic curves are deeply connected to the study of complex numbers and geometry. Using the theory of elliptic functions, mathematicians have shown a unique correspondence. An elliptic curve defined over complex numbers corresponds to an embedding of a torus. A torus is a surface that is topologically shaped like a donut.

Lattice torsion points
Lattice torsion points

This relationship is a group isomorphism, meaning the group structures match perfectly. This connection bridges the gap between algebraic equations and complex geometric shapes. It allows researchers to use tools from one field to solve problems in the other.

The history of these curves is tied to some of the most famous problems in mathematics. Elliptic curves are a central focus in the field of number theory. Most notably, they played a vital role in Andrew Wiles's proof of Fermat's Last Theorem. This was a massive achievement that solved a mystery lasting centuries. Beyond pure math, these curves have practical uses in the modern world. They are used in elliptic curve cryptography, or ECC, to secure digital information. They are also applied in the process of integer factorization.

Researchers also look for specific types of points on these curves, such as rational or integral points. A rational point is a point where the coordinates are rational numbers. The Mordell-Weil theorem states that the group of rational points is finitely generated. This means all rational points can be built from a finite set of starting points.

Elliptic curve on Z61
Elliptic curve on Z61

There are also integral points, where the x-coordinate is an integer. For example, the equation y squared equals x cubed plus 17 has exactly eight integral solutions where y is greater than zero. These specific solutions include pairs like (2, 5) and (43, 282).

It is important to distinguish elliptic curves from standard ellipses. An ellipse is a projective conic and has a genus of zero, whereas an elliptic curve has a genus of one. However, there is a connection in the hyperbolic plane. Real elliptic curves can have a shape that is invariant as ellipses in that specific space. This involves the intersection of a Minkowski hyperboloid with certain quadric surfaces. These intersections produce what are known as Steiner ellipses. This shows that even when names are different, deep mathematical connections often exist between seemingly different shapes.

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Elliptic curve on Z61.svg
File:Elliptic curve on Z89.svg
Elliptic curve on Z89.svg
File:Elliptic curve on Z71.svg
Elliptic curve on Z71.svg
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