"Ample" redirects here. For a definition of the term "ample", see the Wiktionary entry ample.
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In mathematics, a distinctive feature of algebraic geometry is that some line bundles on a projective variety can be considered "positive", while others are "negative" (or a mixture of the two). The most important notion of positivity is that of an ample line bundle, although there are several related classes of line bundles. Roughly speaking, positivity properties of a line bundle are related to having many global sections. Understanding the ample line bundles on a given variety X amounts to understanding the different ways of mapping X into projective space. In view of the correspondence between line bundles and divisors (built from codimension-1 subvarieties), there is an equivalent notion of an ample divisor.
In more detail, a line bundle is called basepoint-free if it has enough sections to give a morphism to projective space. A line bundle is semi-ample if some positive power of it is basepoint-free; semi-ampleness is a kind of "nonnegativity". More strongly, a line bundle on a complete variety X is very ample if it has enough sections to give a closed immersion (or "embedding") of X into projective space. A line bundle is ample if some positive power is very ample.
An ample line bundle on a projective variety X has positive degree on every curve in X. The converse is not quite true, but there are corrected versions of the converse, the Nakai–Moishezon and Kleiman criteria for ampleness.
of an amplelinebundle, although there are several related classes of linebundles. Roughly speaking, positivity properties of a linebundle are related...
a bundle to have no non-zero global sections at all; this is the case for the tautological linebundle. When the linebundle is sufficiently ample this...
called semi-ample if some positive tensor power L ⊗ a {\displaystyle L^{\otimes a}} is basepoint-free. It follows that a semi-amplelinebundle is nef. Semi-ample...
{\displaystyle i^{*}x_{0},\ldots ,i^{*}x_{n}} . Conversely, given an amplelinebundle L → X {\displaystyle {\mathcal {L}}\to X} globally generated by n...
anticanonical bundle is the corresponding inverse bundle ω − 1 {\displaystyle \omega ^{-1}} . When the anticanonical bundle of V {\displaystyle V} is ample, V {\displaystyle...
interpretation of the amplelinebundle over the moduli space of vector bundles on a compact Riemann surface, known as the Quillen determinant linebundle. It can be...
tautological bundle is known as the tautological linebundle. The tautological bundle is also called the universal bundle since any vector bundle (over a compact...
Kodaira embedding theorem claims that a positive linebundle is ample, and conversely, any amplelinebundle admits a Hermitian metric with − 1 Θ {\displaystyle...
varieties, and if L is a big linebundle on X, then f*L is a big linebundle on Y. All amplelinebundles are big. Big linebundles need not determine birational...
geometry. For example, the fact that the canonical bundle is a negative multiple of the amplelinebundle O ( 1 ) {\displaystyle {\mathcal {O}}(1)} means...
canonical linebundle makes projective spaces prime examples of Fano varieties, equivalently, their anticanonical linebundle is ample (in fact very ample). Their...
there exists a very ample sheaf on X relative to S. Indeed, if X is proper, then an immersion corresponding to the very amplelinebundle is necessarily closed...
In algebraic geometry, a Seshadri constant is an invariant of an amplelinebundle L at a point P on an algebraic variety. It was introduced by Demailly...
linearizations of the trivial linebundle. See Example 2.16 of [1] for an example of a variety for which most linebundles are not linearizable. Given an...
third power of an amplelinebundle is normally generated. The Mumford–Kempf theorem states that the fourth power of an amplelinebundle is quadratically...
image D ¯ {\displaystyle {\bar {D}}} is abbreviated with D.) For an amplelinebundle H on S, the definition { H } ⊥ := { D ∈ N u m ( S ) | D ⋅ H = 0 }...
K3 surface together with an amplelinebundle L such that L is primitive (that is, not 2 or more times another linebundle) and c 1 ( L ) 2 = 2 g − 2 {\displaystyle...
the theory of schemes, a related notion is amplelinebundle. (For example, if L is an amplelinebundle, some power of it is generated by global sections...
zero, L {\displaystyle L} is an amplelinebundle on X {\displaystyle X} , and K X {\displaystyle K_{X}} a canonical bundle, then H j ( X , K X ⊗ L ) = 0...
Hilbert polynomial Φ {\displaystyle \Phi } . For a relatively very amplelinebundle L ∈ Pic ( X ) {\displaystyle {\mathcal {L}}\in {\text{Pic}}(X)} and...
irreducible representation as the space of global sections of an amplelinebundle; the highest weight theorem results as a consequence. (The approach...
complete toric variety that has no non-trivial linebundle; thus, in particular, it has no amplelinebundle. Definition 1.1.12 in Ginzburg, V., 1998. Lectures...
Zariski tangent space Function field of an algebraic variety AmplelinebundleAmple vector bundle Linear system of divisors Birational geometry Blowing up...