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Ellipse

For other uses, see Ellipse (disambiguation).

Elliptical redirects here, for the exercise machine, see Elliptical trainer.

The ellipse and some of its mathematical properties.

In mathematics, an ellipse (from the Greek for absence) is a plane algebraic curve where the sum of the distances from any point on the curve to two fixed points is constant. The two fixed points are called foci (plural of focus).

An ellipse is a type of conic section: if a conical surface is cut with a plane which does not intersect the cone's base, the intersection of the cone and plane is an ellipse. For a short elementary proof of this, see Dandelin spheres.

Algebraically, an ellipse is a curve in the Cartesian plane defined by an equation of the form

such that B2 < 4AC, where all of the coefficients are real, and where more than one solution, defining a pair of points (x, y) on the ellipse, exists.

An ellipse can be drawn with two pins, a loop of string, and a pencil. The pins are placed at the foci and the pins and pencil are enclosed inside the string. The pencil is placed on the paper inside the string, so the string is taut. The string will form a triangle. If the pencil is moved around so that the string stays taut, the sum of the distances from the pencil to the pins will remain constant, satisfying the definition of an ellipse.

The line segment which passes through the foci and terminates on the ellipse is called the major axis. The major axis is along the longest segment that passes through the ellipse. The line which passes through the center (halfway between the foci), at right angles to the major axis, is called the minor axis. A semimajor axis is one half the major axis: the line segment from the center, through a focus, and to the edge of the ellipse. Likewise, the semiminor axis is one half the minor axis.

If the two foci coincide, then the ellipse is a circle; in other words, a circle is a special case of an ellipse, one where the eccentricity is zero.

An ellipse centred at the origin can be viewed as the image of the unit circle under a linear map associated with a symmetric matrix A = PDPT, D being a diagonal matrix with the eigenvalues of A, both of which are real positive, along the main diagonal, and P being a real unitary matrix having as columns the eigenvectors of A. Then the axes of the ellipse will lie along the eigenvectors of A, and the squares of the lengths of the axes are the inverses of the eigenvalues.


Parametrisation

The size of an ellipse is determined by two constants, conventionally denoted a and b. The constant a equals the length of the semimajor axis; the constant b equals the length of the semiminor axis.

An ellipse centered at the origin of an x-y coordinate system with its major axis along the x-axis is defined by the equation

The derivation of this formula is quite instructive and not overly difficult.

The following diagram shows an ellipse demonstrating the Pythagoras equation a² = b² + c² as a special case of the non-parametric equation above (x=0, y=b).

The same ellipse is also represented by the parametric equations:

which use the trigonometric functions sine and cosine.

If an ellipse is not centered at the origin of an x-y coordinate system, but again has its major axis along the x-axis, it may be specified by the equation

where (h,k) is the center.

A Gauss-mapped form:

has normal (cosφ,sinφ).

Eccentricity

The shape of an ellipse is usually expressed by a number called the eccentricity of the ellipse, conventionally denoted e (not to be confused with the mathematical constant e). The eccentricity is related to a and b by the statement

or where c (the linear eccentricity of the ellipse) equals the distance from the center to either focus

The eccentricity is a positive number less than 1, or 0 in the case of a circle. The greater the eccentricity is, the larger the ratio of a to b is, and therefore the more elongated the ellipse is. The ellipse shown in the image below has an eccentricity of approximately 0.8733. The distance between the foci is 2ae.

Semi-latus rectum and polar coordinates

The semi-latus rectum of an ellipse, usually denoted (lowercase L), is the distance from a focus of the ellipse to the ellipse itself, measured along a line perpendicular to the major axis. It is related to and (the ellipse's semi-axes) by the formula or, if using the eccentricity, .

In polar coordinates, an ellipse with one focus at the origin and the other on the negative x-axis is given by the equation

An ellipse can also be thought of as a projection of a circle: a circle on a plane at angle φ to the horizontal projected vertically onto a horizontal plane gives an ellipse of eccentricity sin φ, provided φ is not 90°.

Area

The area enclosed by an ellipse is , where π is Archimedes' constant.

Circumference

The circumference of an ellipse is 4aE(e), where the function E is the complete elliptic integral of the second kind.

The exact infinite series is:

A good approximation is Ramanujan's:

which can also be written as:

More generally, the arc length of a portion of the circumference, as a function of the angle subtended, is given by an incomplete elliptic integral. The inverse function, the angle subtended as a function of the arc length, is given by the elliptic functions.

Stretching and Projection

An ellipse may be uniformly stretched along any axis, in or out of the plane of the ellipse, and it will still be an ellipse. The stretched ellipse will have different properties (perhaps changed eccentricity and semi-major axis length, for instance), but it will still be an ellipse (or a degenerate ellipse: a circle or a line). Similarly, any oblique projection onto a plane results in a conic section. If the projection is a closed curve on the plane, then the curve is an ellipse or a degenerate ellipse.

Reflection property

Assume an elliptic mirror with a light source at one of the foci. Then all rays are reflected to a single point — the second focus. Since no other curve has such a property, it can be used as an alternative definition of an ellipse.

Ellipses in physics

Indian astronomer Aryabhata discovered that the orbits of the planets around the sun are ellipses in 499, which he described in his book, the Aryabhatiya [1].

In the 17th century, Johannes Kepler explained that the orbits along which the planets travel around the Sun are ellipses, which is Kepler's first law. Later, Isaac Newton explained this as a corollary of his law of universal gravitation.

More generally, in the gravitational two-body problem, if the two bodies are bound to each other (i.e., the total energy is negative), their orbits are similar ellipses with the common barycenter being one of the foci of each ellipse. Interestingly, the orbit of either body in the reference frame of the other is also an ellipse, with the other body at one focus.

The general solution for a harmonic oscillator in two or more dimensions is also an ellipse, but this time with the origin of the force located at the center of the ellipse.

Albert Einstein also used the ellipse to prove his theory of relativity by using an elliptical shaped mass. Einstein's contributions to modern physics may not have been discovered if it were not for ellipses.

Ellipses in computer graphics

Drawing an ellipse is a common graphics primitive in standard display libraries, such as the QuickDraw and GDI interfaces on the Macintosh and Windows systems. Often such libraries are limited and can only draw an ellipse with either the major axis or the minor axis horizontal.

Jack Bresenham at IBM is most famous for the invention of 2D drawing primitives, including line and circle drawing, using only fast integer operations such as addition and branch on carry bit. An efficient generalization to draw ellipses was invented in 1984 by Jerry Van Aken (IEEE CG&A, Sept. 1984). A more challenging task is to perform these drawing operations with antialiasing, to create a smooth-looking curve. The curve drawing algorithms of Xiaolin Wu (SIGGRAPH 91) are an example.


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The curve drawing algorithms of Xiaolin Wu (SIGGRAPH 91) are an example. Many popular Fleer sets (like "Ultra"), have continued without skipping a year or dramatically changing their design. A more challenging task is to perform these drawing operations with antialiasing, to create a smooth-looking curve. In late 2005 Upper Deck began producing basketball and football cards under it's acquired Fleer name. 1984). In 2004, Fleer announced that it would cease all productions of trading cards. An efficient generalization to draw ellipses was invented in 1984 by Jerry Van Aken (IEEE CG&A, Sept. Fleer and another company, Donruss, were thus allowed to begin making cards in 1981.

Jack Bresenham at IBM is most famous for the invention of 2D drawing primitives, including line and circle drawing, using only fast integer operations such as addition and branch on carry bit. After several years of litigation, the court ordered the union to offer group licenses for baseball cards to companies other than Topps. Often such libraries are limited and can only draw an ellipse with either the major axis or the minor axis horizontal. Topps refused, and Fleer then sued both Topps and the MLBPA to break the Topps monopoly. Drawing an ellipse is a common graphics primitive in standard display libraries, such as the QuickDraw and GDI interfaces on the Macintosh and Windows systems. In April 1975, Fleer asked for Topps to waive its exclusive rights and allow Fleer to produce stickers, stamps, or other small items featuring active baseball players. Einstein's contributions to modern physics may not have been discovered if it were not for ellipses. The union, also fearing that it would cut into existing royalties from Topps sales, then rejected the proposal.

Albert Einstein also used the ellipse to prove his theory of relativity by using an elliptical shaped mass. Topps passed on the opportunity, indicating that it did not think the product would be successful. The general solution for a harmonic oscillator in two or more dimensions is also an ellipse, but this time with the origin of the force located at the center of the ellipse. By now, the MLBPA had settled its differences with Topps and reached an agreement that gave Topps a right of first refusal on such offers. Interestingly, the orbit of either body in the reference frame of the other is also an ellipse, with the other body at one focus. Fleer returned to the union in September 1974 with a proposal to sell 5-by-7-inch satin patches of players, somewhat larger than normal baseball cards. More generally, in the gravitational two-body problem, if the two bodies are bound to each other (i.e., the total energy is negative), their orbits are similar ellipses with the common barycenter being one of the foci of each ellipse. Since this was so far in the future, Fleer declined the proposal.

Later, Isaac Newton explained this as a corollary of his law of universal gravitation. The MLBPA was in a dispute with Topps over player contracts, and offered Fleer the exclusive rights to market cards of most players starting in 1973, when many of Topps's contracts would expire. In the 17th century, Johannes Kepler explained that the orbits along which the planets travel around the Sun are ellipses, which is Kepler's first law. In 1968, Fleer was approached by the Major League Baseball Players Association, a recently organized players' union, about obtaining a group license to produce cards. Indian astronomer Aryabhata discovered that the orbits of the planets around the sun are ellipses in 499, which he described in his book, the Aryabhatiya [1]. The decision gave Topps an effective monopoly of the baseball card market. Since no other curve has such a property, it can be used as an alternative definition of an ellipse. However, Fleer chose not to pursue such options and instead sold its remaining player contracts to Topps for $395,000 in 1966.

Then all rays are reflected to a single point — the second focus. The Commission concluded that because the contracts only covered the sale of cards with gum, competition was still possible by selling cards with other small, low-cost products. Assume an elliptic mirror with a light source at one of the foci. A hearing examiner ruled against Topps in 1965, but the Commission reversed this decision on appeal. If the projection is a closed curve on the plane, then the curve is an ellipse or a degenerate ellipse. The complaint focused on the baseball card market, alleging that Topps was engaging in unfair competition through its aggregation of exclusive contracts. Similarly, any oblique projection onto a plane results in a conic section. The company now turned its efforts to supporting an administrative complaint filed against Topps by the Federal Trade Commission.

The stretched ellipse will have different properties (perhaps changed eccentricity and semi-major axis length, for instance), but it will still be an ellipse (or a degenerate ellipse: a circle or a line). This left Fleer with no product in either baseball or football. An ellipse may be uniformly stretched along any axis, in or out of the plane of the ellipse, and it will still be an ellipse. In 1964, however, Philadelphia Gum secured the rights for NFL cards and Topps took over the AFL. The inverse function, the angle subtended as a function of the arc length, is given by the elliptic functions. The next year reverted to the status quo, with Fleer covering the AFL and Topps the NFL. More generally, the arc length of a portion of the circumference, as a function of the angle subtended, is given by an incomplete elliptic integral. In 1961, each company produced cards featuring players from both leagues.

which can also be written as:. Fleer produced a set for the AFL while Topps cards covered the established National Football League. A good approximation is Ramanujan's:. Meanwhile, Fleer took advantage of the emergence of the American Football League in 1960 to begin producing football cards. The exact infinite series is:. However, Topps still held onto the rights of most players and the set was not particularly successful. The circumference of an ellipse is 4aE(e), where the function E is the complete elliptic integral of the second kind. Wills and Jimmy Piersall served as player representatives for Fleer, helping to bring others on board.

The area enclosed by an ellipse is , where π is Archimedes' constant. This 67-card set included a number of stars, including 1962 National League MVP Maury Wills (then holder of the modern record for stolen bases in a season), who had elected to sign with Fleer instead of Topps. An ellipse can also be thought of as a projection of a circle: a circle on a plane at angle φ to the horizontal projected vertically onto a horizontal plane gives an ellipse of eccentricity sin φ, provided φ is not 90°. The company did not produce new cards the next year, but continued selling the 1961 set while it focused on signing enough players to produce a set featuring active players in 1963. In polar coordinates, an ellipse with one focus at the origin and the other on the negative x-axis is given by the equation. One set was produced in 1960 and a second in 1961. It is related to and (the ellipse's semi-axes) by the formula or, if using the eccentricity, . However, Fleer continued to produce baseball cards by featuring Williams with other mostly retired players in a Baseball Greats series.

The semi-latus rectum of an ellipse, usually denoted (lowercase L), is the distance from a focus of the ellipse to the ellipse itself, measured along a line perpendicular to the major axis. Williams was nearing the end of his career and retired after the 1960 season. The distance between the foci is 2ae. Fleer was unable to include other players because another company, Topps, had signed most active baseball players to exclusive contracts. The ellipse shown in the image below has an eccentricity of approximately 0.8733. It began by signing baseball star Ted Williams to a contract in 1959 and sold an 80-card set oriented around highlights of his career. The greater the eccentricity is, the larger the ratio of a to b is, and therefore the more elongated the ellipse is. Well-established as a gum and candy company, Fleer followed some of its competitors into the business of selling sports cards.

The eccentricity is a positive number less than 1, or 0 in the case of a circle. One negative aspect associated with Fleer's bankruptcy is that many sports card collectors now own redemption cards for autographs and memorabilia that may not be able to be redeemed. or where c (the linear eccentricity of the ellipse) equals the distance from the center to either focus. Competitor Upper Deck won the Fleer name, as well as their die cast toy business, at a price of $6.1 million. The eccentricity is related to a and b by the statement. The move included the auction of the Fleer trade name, as well as other holdings. The shape of an ellipse is usually expressed by a number called the eccentricity of the ellipse, conventionally denoted e (not to be confused with the mathematical constant e). By early July, in a move similar to declaring bankruptcy, the company began to liquidate its assets to repay creditors.

has normal (cosφ,sinφ). In late May 2005, news circulated that Fleer was suspending its trading card operations immediately. A Gauss-mapped form:. In 1998, 70-year-old Dubble Bubble was acquired by Canadian company Concord Confections and Concord, in turn, was acquired by Chicago-based Tootsie Roll Industries in 2004. where (h,k) is the center. In 1995, Fleer acquired the trading card company SkyBox International and it closed its Philadelphia plant(where Dubble Bubble was made for 67 years). If an ellipse is not centered at the origin of an x-y coordinate system, but again has its major axis along the x-axis, it may be specified by the equation. Fleer became known as a maker of sports cards, and has also produced some non-sports trading cards.

which use the trigonometric functions sine and cosine. Its pink color set a tradition for nearly all bubble gums to follow. The same ellipse is also represented by the parametric equations:. In 1928, Fleer employee Walter Diemer improved the Blibber-Blubber formulation to produce the first commercially successful bubblegum, Dubble Bubble. The following diagram shows an ellipse demonstrating the Pythagoras equation a² = b² + c² as a special case of the non-parametric equation above (x=0, y=b). Unfortunately, while this gum was capable of being blown into bubbles, in other respects it was vastly inferior to regular chewing gum, and Blibber-Blubber was never marketed to the public. The derivation of this formula is quite instructive and not overly difficult. Fleer originally developed a bubblegum formulation called Blibber-Blubber in 1906.

An ellipse centered at the origin of an x-y coordinate system with its major axis along the x-axis is defined by the equation. Bought out by comic-book empire Marvel in 1992, it is now a part of Upper Deck. The constant a equals the length of the semimajor axis; the constant b equals the length of the semiminor axis. Fleer in the mid-19th century, was the first company to successfully manufacture bubblegum. The size of an ellipse is determined by two constants, conventionally denoted a and b. The Fleer Corporation, founded by Frank H. .


. Then the axes of the ellipse will lie along the eigenvectors of A, and the squares of the lengths of the axes are the inverses of the eigenvalues. An ellipse centred at the origin can be viewed as the image of the unit circle under a linear map associated with a symmetric matrix A = PDPT, D being a diagonal matrix with the eigenvalues of A, both of which are real positive, along the main diagonal, and P being a real unitary matrix having as columns the eigenvectors of A. If the two foci coincide, then the ellipse is a circle; in other words, a circle is a special case of an ellipse, one where the eccentricity is zero.

Likewise, the semiminor axis is one half the minor axis. A semimajor axis is one half the major axis: the line segment from the center, through a focus, and to the edge of the ellipse. The line which passes through the center (halfway between the foci), at right angles to the major axis, is called the minor axis. The major axis is along the longest segment that passes through the ellipse.

The line segment which passes through the foci and terminates on the ellipse is called the major axis. If the pencil is moved around so that the string stays taut, the sum of the distances from the pencil to the pins will remain constant, satisfying the definition of an ellipse. The string will form a triangle. The pencil is placed on the paper inside the string, so the string is taut.

The pins are placed at the foci and the pins and pencil are enclosed inside the string. An ellipse can be drawn with two pins, a loop of string, and a pencil. such that B2 < 4AC, where all of the coefficients are real, and where more than one solution, defining a pair of points (x, y) on the ellipse, exists. Algebraically, an ellipse is a curve in the Cartesian plane defined by an equation of the form.

For a short elementary proof of this, see Dandelin spheres. An ellipse is a type of conic section: if a conical surface is cut with a plane which does not intersect the cone's base, the intersection of the cone and plane is an ellipse. The two fixed points are called foci (plural of focus). In mathematics, an ellipse (from the Greek for absence) is a plane algebraic curve where the sum of the distances from any point on the curve to two fixed points is constant.

Elliptical redirects here, for the exercise machine, see Elliptical trainer..