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Twisted cubic

In algebraic geometry, the twisted cubic is a smooth, rational curve of degree three embedded in three-dimensional projective space \mathbb{P}^3, serving as a fundamental example of a skew curve that does not lie in any plane.^[1] It can be parametrized affinely as (t, t^2, t^3) for t \in \mathbb{R} or, more generally, projectively via the Veronese map \nu: \mathbb{P}^1 \to \mathbb{P}^3 sending [t_0 : t_1] \mapsto [t_0^3 : t_0^2 t_1 : t_0 t_1^2 : t_1^3].^[1]^[2] This embedding arises from the complete linear system of degree-three divisors on \mathbb{P}^1, making the curve isomorphic to the projective line \mathbb{P}^1.^[3] The twisted cubic has roots in classical geometry, with early connections to problems like duplicating the cube traced to Menaechmus around 380–320 BCE, though it was formally studied in the 19th century by mathematicians such as August Ferdinand Möbius (1827), Michel Chasles, and George Salmon, who named it.^[1] As an ideal example in modern algebraic geometry, it illustrates key concepts like free resolutions of ideals and the Hilbert-Burch theorem, where its homogeneous ideal is generated by three quadrics: x_0 x_2 - x_1^2 = 0, x_0 x_3 - x_1 x_2 = 0, and x_1 x_3 - x_2^2 = 0 in homogeneous coordinates [x_0 : x_1 : x_2 : x_3].^[1]^[2] These equations define it as the intersection of three quadric surfaces, and it lies on the quadric hypersurface given by x_0 x_3 - x_1 x_2 = 0.^[2] Notable properties include its degree-three nature, meaning it intersects a general hyperplane in three points, and the fact that any four points on it span \mathbb{P}^3 while it passes through any six points in general position no three of which are collinear.^[1] Beyond pure mathematics, the twisted cubic appears in applications such as Bézier curves in computer graphics for modeling smooth paths and in statistical models for binomial probabilities.^[1] Its study also connects to intersection theory, secant varieties, and projections that yield singular plane cubics like nodal or cuspidal curves.^[3]

Definition and Parametrization

Parametric Form

The twisted cubic curve in affine 3-space \mathbb{A}^3 is given by the parametric equations

\gamma(t) = (t, t^2, t^3), \quad t \in \mathbb{R}.

This parametrization traces a space curve that spirals along the x-axis without lying in any plane, providing a concrete visualization of its skew nature.^[1] In projective 3-space \mathbb{P}^3, the twisted cubic arises as the image of the Veronese embedding of degree 3, defined by the map

\nu: \mathbb{P}^1 \to \mathbb{P}^3, \quad [s:t] \mapsto [s^3 : s^2 t : s t^2 : t^3].

This morphism embeds the projective line \mathbb{P}^1 as a curve of degree 3 in \mathbb{P}^3, where the degree corresponds to the highest power in the homogeneous coordinates.^[4] The parametric form via the Veronese map demonstrates that the twisted cubic is a rational curve, birational to \mathbb{P}^1 through this embedding, which is an isomorphism onto its image.^[5] This rationality facilitates computations in algebraic geometry, such as resolving its ideal or studying its intersections.

Implicit Equations

The twisted cubic curve in projective 3-space \mathbb{P}^3 with homogeneous coordinates [x_0 : x_1 : x_2 : x_3] is defined as the algebraic variety V(I), where I is the homogeneous prime ideal generated by the $2 \times 2 minors of the matrix

\begin{pmatrix} x_0 & x_1 & x_2 \\ x_1 & x_2 & x_3 \end{pmatrix}.

These minors yield the three quadratic equations \begin{align*} x_0 x_2 - x_1^2 &= 0, \ x_0 x_3 - x_1 x_2 &= 0, \ x_1 x_3 - x_2^2 &= 0. \end{align*} The common zeros of these equations in \mathbb{P}^3 form the twisted cubic, as the ideal I is prime and the variety is irreducible.^[1]^[6] This matrix representation arises from the structure of the twisted cubic's parametrization, where the coordinates correspond to moments or coefficients that align with a Hankel matrix form, in which entries are constant along anti-diagonals. Such Hankel matrices commonly appear in the implicitization of rational curves via determinantal ideals, capturing the rank condition (here, rank at most 1) that defines the variety.^[1] To verify that these equations define a curve of degree 3, note that a general hyperplane in \mathbb{P}^3 intersects V(I) in exactly three points (counting multiplicity), consistent with Bézout's theorem applied to the resulting system, and the variety matches the known parametric embedding of degree 3. The parametric form [1 : t : t^2 : t^3] satisfies these equations for all t, confirming they capture the curve without extraneous components.^[1]

Geometric Properties

Planarity and Skew Nature

The twisted cubic curve, embedded in three-dimensional projective space \mathbb{P}^3, is fundamentally non-planar, meaning it does not lie in any plane. This non-planarity distinguishes it from lower-degree curves, such as conics, which always reside in a plane. To see this, consider the parametric embedding given by [s:t] \mapsto [s^3 : s^2 t : s t^2 : t^3], which maps the projective line \mathbb{P}^1 into \mathbb{P}^3. Suppose for contradiction that the image lies in a hyperplane defined by a linear equation a x_0 + b x_1 + c x_2 + d x_3 = 0. Substituting the parametric form yields a cubic equation in the ratio u = s/t (assuming t \neq 0), which would vanish identically only if all coefficients are zero, but explicit computation shows the coefficients a + b u + c u^2 + d u^3 form a non-trivial cubic polynomial with roots, implying only finitely many points satisfy it rather than the entire curve. Thus, no such hyperplane contains the curve.^[7] A concrete demonstration of non-planarity involves selecting four distinct points on the curve and verifying they are not coplanar. For the affine portion parametrized by (u, u^2, u^3) with u \in \mathbb{R}, take points at u = 0 giving (0,0,0), u=1 giving (1,1,1), u=2 giving (2,4,8), and u=-1 giving (-1,1,-1). These points span \mathbb{R}^3 if the determinant of the matrix formed by their position vectors (relative to one point) is non-zero: computing the scalar triple product or volume yields a non-zero value (specifically, -12), confirming they are not coplanar. Since any plane containing the curve would contain all points, including these four, the curve cannot lie in a plane. This property holds projectively as well, with any four points on the twisted cubic spanning the full \mathbb{P}^3.^[7]^[1] The skew nature of the twisted cubic arises from its embedding in \mathbb{P}^3 without lying in any hyperplane, making it a prototypical skew curve. The twisted cubic admits no trisecant lines, so any line in \mathbb{P}^3 intersects the curve in at most two points (counting distinct points); a general line intersects it in zero points. This property highlights its twisted embedding, avoiding the triple intersections possible for some non-skew curves. The secant variety, formed by the union of all secant lines (chords joining two points on the curve) and tangent lines, fills the entire \mathbb{P}^3; moreover, every point in \mathbb{P}^3 not on the curve lies on a unique such line, highlighting the dense spatial occupation by these chords.^[7] In differential geometric terms, the non-planarity manifests through non-zero torsion along the curve. For the affine parametrization \mathbf{r}(t) = (t, t^2, t^3), the torsion is given by

\tau(t) = \frac{3}{9t^4 + 9t^2 + 1},

which is positive and non-zero for all real t. This contrasts with planar curves, where torsion vanishes identically by the Frenet-Serret theorem, as the binormal vector remains constant. The non-vanishing torsion quantifies the curve's twisting out of any plane, providing a local measure of its skew configuration.

Intersections and Tangents

The twisted cubic curve, being a degree 3 variety in projective 3-space \mathbb{P}^3, intersects any plane (a degree 1 hypersurface) in exactly 3 points, counting multiplicities, as dictated by the generalized Bézout theorem for intersections in projective space.^[2]^[8] This transversality highlights the curve's general position, where generic planes cut it transversally at three distinct points, while special planes may exhibit tangencies or inflections at the intersection loci. The tangent line to the twisted cubic at a parameter value t is the line passing through the point \gamma(t) = (t, t^2, t^3) with direction given by the derivative \gamma'(t) = (1, 2t, 3t^2).^[1] In projective terms, this corresponds to the line joining [1 : t : t^2 : t^3] and the point at infinity determined by the direction vector. These tangents envelop a ruled surface known as the tangent developable, which fills a portion of the ambient space without containing the curve itself beyond the point of tangency. The osculating plane at parameter t is the plane spanned by the position vector \gamma(t), the tangent vector \gamma'(t), and the second derivative \gamma''(t) = (0, 2, 6t), providing the best quadratic approximation to the curve at that point.^[9] These planes vary continuously along the curve; their union forms the osculating developable surface, and they are related to the ruled structure of the quadric hypersurface containing the twisted cubic. Their envelope defines the curve's dual geometry. A defining geometric feature of the twisted cubic is that no three distinct points on it are collinear, meaning it admits no trisecant lines; any line intersects the curve in at most two points.^[10] Consequently, any three distinct points on the curve determine a unique plane that intersects the twisted cubic precisely at those three points, underscoring its role as a rational normal curve of degree 3.^[11]

Algebraic Properties

Ideal Structure

The prime ideal I defining the twisted cubic curve in the projective space \mathbb{P}^3 over an algebraically closed field k is the homogeneous ideal in the polynomial ring k[x_0, x_1, x_2, x_3] generated by the three quadratic polynomials

x_0 x_2 - x_1^2, \quad x_0 x_3 - x_1 x_2, \quad x_1 x_3 - x_2^2.

These generators arise as the $2 \times 2 minors of the catalecticant matrix associated with the parametrization and fully determine the ideal membership for the curve.^[12] The ideal I is prime, reflecting the irreducibility of the twisted cubic as a variety.^[13] This ideal structure underscores the toric nature of the twisted cubic, as I is precisely the kernel of the surjective k-algebra homomorphism \phi: k[x_0, x_1, x_2, x_3] \to k[s^3, s^2 t, s t^2, t^3] defined by x_0 \mapsto s^3, x_1 \mapsto s^2 t, x_2 \mapsto s t^2, and x_3 \mapsto t^3. This map encodes the twisted cubic as a monomial curve, where the target ring is generated by the monomials s^3, s^2 t, s t^2, t^3 of total degree 3 in s and t.^[14] The variety V(I) thus has dimension 1 and codimension 2 in \mathbb{P}^3, consistent with its embedding as a curve in three-dimensional projective space.^[15] The Hilbert polynomial of the coordinate ring k[x_0, x_1, x_2, x_3]/I is $3t + 1, where the leading coefficient 3 gives the degree of the curve and the constant term indicates arithmetic genus 0. This polynomial confirms the rationality of the twisted cubic, as it is isomorphic to \mathbb{P}^1.^[15] The three quadratic generators minimally generate the ideal, and the relations among them highlight the non-free structure of the syzygies.^[12]

Resolutions and Embeddings

The ideal of the twisted cubic in the polynomial ring S = k[x_0, x_1, x_2, x_3] over an algebraically closed field k admits a minimal free resolution of the quotient S/I that is linear after the first step, meaning each subsequent free module is shifted by successive degrees. Specifically, the resolution takes the form

$0 \to S(-3)^2 \to S(-2)^3 \to S \to S/I \to 0,

where I is generated by three quadrics, and the map from S(-2)^3 to S is given by the generators of I. The Betti numbers of this resolution are \beta_0 = 1, \beta_1 = 3, and \beta_2 = 2, reflecting the ranks of the free modules involved. This structure arises from the Hilbert-Burch theorem, which characterizes perfect ideals of codimension 2 and guarantees that the syzygy module of I is free, with the first syzygies generated by linear relations among the quadratic generators of I. The twisted cubic serves as the degree-3 case of the rational normal curve, obtained via the Veronese embedding \nu_d: \mathbb{P}^1 \to \mathbb{P}^d that maps [t_0 : t_1] \mapsto [t_0^d : t_0^{d-1} t_1 : \cdots : t_1^d]. For d=3, this embeds \mathbb{P}^1 into \mathbb{P}^3 as a curve of degree 3, generalizing to higher dimensions where the image is a nondegenerate curve of degree d spanning \mathbb{P}^d. A key embedding property is that no four points on the twisted cubic are coplanar; equivalently, any four distinct points span the full \mathbb{P}^3, ensuring the curve's nondegeneracy and minimal embedding dimension.^[1]

Historical Context

Ancient Origins

The problem of duplicating the cube, one of the three classical problems of antiquity, provided early conceptual precursors to the twisted cubic through geometric constructions aimed at finding mean proportionals. Hippocrates of Chios (ca. 470–410 BCE) first reduced the duplication to the task of inserting two geometric mean proportionals between two line segments of lengths a and b = 2a, such that a : x = x : y = y : b, which implies x^3 = a^2 b or equivalently y^3 = a b^2. This reformulation shifted focus from direct volume construction to proportional lengths, implicitly involving cubic relations without algebraic notation.^[16]^[17] Menaechmus (ca. 380–320 BCE), a pupil of Plato, advanced this by employing intersections of conic sections to solve for the mean proportionals, crediting him with the discovery of conics in this context. In one solution, he intersected a parabola y^2 = b x with a hyperbola x y = a b, yielding the required proportions; another used two parabolas y^2 = b x and x^2 = a y. These constructions geometrically generate points satisfying cubic equations like x^3 = a b^2 via the intersection of quadratic curves, effectively tracing loci that retrospectively align with the twisted cubic's path in space.^[17]^[1] Ancient Greek mathematicians did not provide an explicit parametrization of such curves, emphasizing instead geometric loci and intersections of conics or quadrics as tools for problem-solving rather than studying the curves as algebraic objects. Their approach relied on planar diagrams and proportional constructions, viewing the relevant space curve as an incidental outcome of solving for lengths in three dimensions.^[1]^[17] These early efforts prefigured later systematic studies of quadric intersections and space curves, influencing the development of projective geometry and the explicit recognition of the twisted cubic in the 19th century.^[1]

Modern Developments

In the 19th century, the twisted cubic received systematic study within the framework of projective geometry, building on ancient precursors such as the cissoid and conchoid curves. Ferdinand Möbius (1790–1868) was the first to examine it rigorously, introducing barycentric coordinates and analyzing its properties as a curve in projective space in his 1827 work Der barycentrische Calcül.^[1] Möbius's approach highlighted its role as a non-planar rational curve of degree three, distinct from plane cubics. Michel Chasles (1793–1880) also made important early contributions concerning twisted cubics. Later, George Salmon (1819–1904) formalized its nomenclature and properties in his seminal text A Treatise on the Analytic Geometry of Three Dimensions, first published in 1865, where he coined the term "twisted cubic" to emphasize its skew nature in three-dimensional space.^[18] David Hilbert's 1890 paper "Über die Theorie der algebraischen Formen" marked a pivotal advancement, employing the twisted cubic as a key example in developing the basis theorem for ideals in polynomial rings and exploring free resolutions in invariant theory. Hilbert demonstrated that the ideal of the twisted cubic admits a finite basis of quadratic generators, proving the Noetherian property of polynomial rings and laying groundwork for commutative algebra; this resolution structure, now known via the Hilbert-Burch theorem, underscored the curve's utility in resolving syzygies.^[1] In the 20th century, the twisted cubic gained prominence in algebraic geometry through its parametrization in the Hilbert scheme. The component of the Hilbert scheme \Hilb^{3t+1}(\mathbb{P}^3) corresponding to degree-three rational curves is irreducible and smooth of dimension 12, with the open dense subset consisting of twisted cubics, as shown by Piene and Schlessinger in their 1985 study of its compactification.^[19] Additionally, in differential geometry, the Frenet-Serret apparatus, developed by Jean Frédéric Frenet in 1847 and Joseph Alfred Serret in 1851, positioned the twisted cubic as the universal local model for space curves, approximating the osculating behavior near a general point via curvature and torsion.^[1]

Applications

Differential Geometry

The twisted cubic curve, parametrized by \gamma(t) = (t, t^2, t^3), serves as a fundamental example in the differential geometry of space curves due to its non-planar nature and non-vanishing torsion. Its Frenet-Serret apparatus provides insight into its local geometry through the unit tangent vector T(t), principal normal N(t), and binormal B(t), which satisfy the structure equations \frac{dT}{ds} = \kappa N, \frac{dN}{ds} = -\kappa T + \tau B, and \frac{dB}{ds} = -\tau N, where s is the arc-length parameter, \kappa is the curvature, and \tau is the torsion.^[20]^[21] For the twisted cubic, the curvature is given by

\kappa(t) = \frac{2 \sqrt{9t^4 + 9t^2 + 1}}{(1 + 4t^2 + 9t^4)^{3/2}},

and the torsion by

\tau(t) = \frac{3}{9t^4 + 9t^2 + 1}.

These expressions highlight the curve's varying bending and twisting: at t = 0, \kappa(0) = 2 and \tau(0) = 3, indicating significant initial curvature and torsion, while both decrease as |t| increases.^[20]^[21] The twisted cubic acts as a universal local model for any smooth space curve near points of non-zero torsion. By the fundamental theorem of space curves, any such curve can be locally reparametrized by arc length s and rigidly transformed to match the Taylor expansion of the twisted cubic up to third order: x(s) = s - \frac{1}{6} \kappa s^3 + O(s^4), y(s) = \frac{1}{2} \kappa s^2 + O(s^4), z(s) = -\frac{1}{6} \kappa \tau s^3 + O(s^4), where the coefficients depend on the local \kappa and \tau. This equivalence underscores the twisted cubic's role in classifying local curve geometry via curvature and torsion invariants.^[1] The osculating circle at any point lies in the osculating plane spanned by T and N, with radius $1/\kappa(t), approximating the curve to second order. The osculating sphere, which approximates to third order, passes through the point and matches the first three derivatives, but along the twisted cubic, the osculating plane itself twists due to non-zero \tau, preventing the curve from lying in a fixed plane or sphere globally.^[20] This geometric framework originated in the 1850s with the independent works of Joseph Alfred Serret and Jean Frédéric Frenet, who developed the Frenet-Serret formulas and used cubic parametrizations similar to the twisted cubic to illustrate the interplay of curvature and torsion in space curves.^[1]

Algebraic Statistics and Graphics

In algebraic statistics, the twisted cubic serves as a rational normal curve that parametrizes the probability distribution of a binomial random variable with three independent trials, where the coordinates correspond to the probabilities of observing 0, 1, 2, or 3 successes via the map (p_0, p_1, p_2, p_3) = (t^3, 3t^2(1-t), 3t(1-t)^2, (1-t)^3) for t \in [0,1].^[22] This model falls under toric statistical models, with the associated toric ideal generated by quadratic binomials such as p_0 p_2 - p_1^2, p_0 p_3 - p_1 p_2, and p_1 p_3 - p_2^2, enabling computations like Markov bases for sampling from conditional distributions as introduced by Diaconis and Sturmfels.^[23] The secant variety of the twisted cubic arises in mixture models and hidden variable frameworks, parametrizing distributions that are convex combinations of points on the curve, which aids in likelihood inference for unobserved data structures.^[22] For instance, in toric ideals related to hidden Markov models, the twisted cubic provides an algebraic framework for computing invariants and testing model fit through Gröbner bases of the ideal.^[22] In computer graphics and computer-aided geometric design (CAGD), projections of the twisted cubic onto a plane yield cubic Bézier curves, which are parametric curves defined by four control points p_0, p_1, p_2, p_3 and Bernstein basis polynomials:

\mathbf{B}(t) = (1-t)^3 p_0 + 3(1-t)^2 t p_1 + 3(1-t) t^2 p_2 + t^3 p_3, \quad t \in [0,1].

These curves, developed by Pierre Bézier in the 1960s for automotive design at Renault, enable smooth interpolation and are widely used in font outlining (e.g., in TrueType and PostScript systems) and keyframe animation paths for fluid motion.^[1] Implicitization techniques in CAGD convert such parametric representations of cubic curves to implicit polynomial equations, facilitating efficient intersection algorithms between curves or with surfaces in rendering pipelines; for the twisted cubic, this yields the ideal \langle x_0 x_2 - x_1^2, x_0 x_3 - x_1 x_2, x_1 x_3 - x_2^2 \rangle in projective space, which serves as a model for these computations.^[24]

References

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[PDF] The many lives of the twisted cubic - Mathematics & Computer Science
Feb 10, 2018 · Abstract. We trace some of the history of the twisted cubic curves in three-dimensional affine and projective spaces.
[2]
[PDF] Algebraic Geometry - Berkeley Math Circle
The twisted cubic curve C is the zero locus of three polynomials: C = Z(Z0Z3 − Z1Z2,Z0Z2 − Z2. 1 ,Z1Z3 − Z2. 2 ). The twisted cubic C lies on the quadric ...
[3]
[PDF] FOUNDATIONS OF ALGEBRAIC GEOMETRY PROBLEM SET 7
Nov 9, 2007 · ... curve in P3 k. This curve is called the twisted cubic. The twisted cubic is a good non-trivial example of many things, so it you should make ...
[4]
[PDF] The geometry of marked contact Engel structures - arXiv
Sep 17, 2018 · γ = [s3,s2t, st2,t3]. Denoting by (E1,E2,E3,E4) the dual basis, the twisted cubic is also given by the zero set of the three.
[5]
[PDF] The space of twisted cubics - research.chalmers.se
isomorphic to the twisted cubic component of the Hilbert scheme. A twisted cubic is a smooth rational curve of degree three. The family of such curves in P3 ...
[6]
[PDF] Geometry of Algebraic Curves
We thus get a curve in the dual projective space, which we can call the dual curve. Let's give an example. Take C ⊂ P3 a twisted cubic curve. What's the dual ...
[7]
[PDF] pdf - CSE IITB
... 4. Joe Harris. Algebraic Geometry. A First Course. With 83 Illustrations. Springer Science+Business Media, LLC. Page 5. Joe Harris. Department of Mathematics.
[8]
[PDF] DIFFERENTIAL GEOMETRY: A First Course in Curves and Surfaces
... twisted cubic (see Example 1(e)) lie on a plane. 13. Consider the “spiral ... Prove that the torsion of ˛ and the torsion of. ˇ at corresponding points have ...
[9]
[PDF] an arithmetic enrichment of bézout's theorem - Stephen McKean
In this paper, we study the intersections of n hypersurfaces in projective n-space over an arbitrary perfect field k. Classically, Bézout's Theorem addresses ...
[10]
ON TWISTED CUBIC CURVES THAT HAVE A DIRECTRIX*
The osculating planes of a twisted cubic form a developable of order 4 and class 3 ; that is, through every point of space there pass three planes of the.
[11]
[PDF] arXiv:1909.03811v2 [math.AG] 27 May 2020
May 27, 2020 · Example 2.8 (Twisted cubic). If (d, g) = (3,0), then X is the twisted cubic, which has no trisecant line. Indeed, the ideal of the twisted ...
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[PDF] ON THE SINGULARITIES OF THE TRISECANT SURFACE TO A ...
The twisted cubic C has no trisecant lines: C is cut out by quadrics. (the 2 × 2-minors of a 2 × 3 matrix with linear entries), thus it has no trisecant line ...
[13]
[PDF] Basic Algebraic Geometry Example Sheet 2
(2) Let C ⊂ P3 be the twisted cubic curve, that is, the image of P1 under the morphism. (x0,x1,x2,x3)=(t3. 0,t2. 0t1,t0t2. 1,t3. 1). The purpose of the next ...
[14]
[PDF] distributions via hilbert schemes
ideal is prime because the natural inclusion ψ : C[x1] ,→ C[x1,x2,x3]/(x2 ... twisted cubic curve, which has ideal. I = (x0x2 − x2. 1,x0x3 − x1x2,x1x3 ...
[15]
[PDF] interactive tutorial: macaulay2 day at the fields institute
Create the homogeneous ideal of the twisted cubic curve in four different ways—as the kernel of a ring map, via elimination, using the monomialCurveIdeal.
[16]
[PDF] FOUNDATIONS OF ALGEBRAIC GEOMETRY CLASS 31
Feb 14, 2006 · Show that the twisted cubic (in P3) has Hilbert polynomial 3m + 1. 1.4. Exercise. Find the Hilbert polynomial for the dth Veronese embedding ...
[17]
Hippocrates - Biography - MacTutor - University of St Andrews
Hippocrates also showed that a cube can be doubled if two mean proportionals can be determined between a number and its double. This had a major influence on ...
[18]
Doubling the cube - MacTutor History of Mathematics
Menaechmus is said to have made his discovery of conic sections while he was attempting to solve the problem of doubling the cube. Menaechmus's solution to ...Missing: twisted | Show results with:twisted
[19]
The Many Lives of the Twisted Cubic - jstor
It is not hard to see that the twisted cubic coincides with the intersection of the three quadric surfaces. These implicit equations of the curve will reappear ...<|control11|><|separator|>
[20]
On the Hilbert Scheme Compactification of the Space of Twisted ...
A twisted cubic curve is a rational, smooth curve of degree 3 in P3. The space Ho of such curves has the structure of a smooth, 12-dimensional, noncompact ...
[21]
[PDF] Curves - Lia Vas
curve from (4). 7. Find the Frenet-Serret apparatus for the twisted cubic (t, t2,t3). Solutions. 1. γ0 = (1,2t,3t2), |γ0| = √. 1+4t2 + 9t4, γ00 = (0,2,6t) ...
[22]
Space Curves, Frenet Frames, and Torsion - UMD MATH
We calculate the Frenet frame for the twisted cubic: tcvel=diff(twistcube) ... Thus we have the Frenet-Serret formulae: The last of these is easily ...
[23]
Algebraic statistics [draft ed.] - DOKUMEN.PUB
Every point on the twisted cubic satisfies the equations p21 = p2 and p31 = p3 , and conversely every point satisfying these two equations is in the image of ...
[24]
Algebraic algorithms for sampling from conditional distributions
February 1998 Algebraic algorithms for sampling from conditional distributions. Persi Diaconis, Bernd Sturmfels · DOWNLOAD PDF + SAVE TO MY LIBRARY. Ann ...
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[PDF] Curves and Surfaces in Geometric Modeling: Theory and Algorithms
... (CAGD), but our goal is not to write another text on CAGD. In brief, we are ... twisted cubic curve. Given any four pairwise distinct values t1,t2,t3,t4 ...