T x I
triangulations that typically appear at the centres of layered torus bundles.
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#include <ntxicore.h>
Inheritance diagram for regina::NTxIDiagonalCore:
Public Member Functions | |
NTxIDiagonalCore (unsigned long newSize, unsigned long newK) | |
Creates a new T x I triangulation with the given parameters. | |
unsigned long | size () const |
Returns the total number of tetrahedra in this T x I triangulation. | |
unsigned long | k () const |
Returns the additional parameter k as described in the class notes. | |
std::ostream & | writeName (std::ostream &out) const |
Writes the name of this specific triangulation of T x I to the given output stream. | |
std::ostream & | writeTeXName (std::ostream &out) const |
Writes the name of this specific triangulation of T x I in TeX format to the given output stream. |
T x I
triangulations that typically appear at the centres of layered torus bundles.
Different triangulations in this family use different numbers of tetrahedra, with the larger triangulations producing more complicated relationships between the upper and lower boundary curves.
Members of this family are parameterised by their size (the number of tetrahedra) and an additional integer k, where 1 <= k <= size - 5. Note that this means we must have size >= 6. The member of this family of size n with additional parameter k is labelled T_n:k
.
It is worth noting that T_n:k
is isomorphic to T_n:(n-4-k)
, so in reality there are only [(n-4)/2] different triangulations for a given size (rounded down).
A triangulation of this family is most easily defined in terms of its central torus. Central surfaces are described in detail in "Structures of small closed non-orientable 3-manifold triangulations" (Burton 2003, to appear in J. Knot Theory Ramifications, math.GT/0311113); in particular, see the section on thin I-bundles.
The central torus begins with two triangles u0 and u1 (which eventually provide the upper torus boundary), with a chain of quadrilaterals q1, ..., q(n-5) descending diagonally beneath them as illustrated in the diagram below.
We then distort quadrilateral qk and attach two more triangles w0 and w1 to its side (these will eventually provide the lower torus boundary). This is illustrated in the following diagram.
The entire central torus wraps from left to right (so the lower left edges of most quadrilaterals qi are identified with the upper right edges of q(i-1), and the left edge of qk is identified with the right edge of w1). As an exception, the two uppermost edges are identified with the two lowermost edges in a parallel fashion (so the upper left edge of u1 is identified with the lower right edge of q1, and the adjacent edges at right angles to these are also identified).
The four triangles in the central torus correspond to the four tetrahedra in the triangulation that provide the boundary faces. The upper boundary is coned out from triangles u0 and u1, and the lower boundary is coned out from triangles w0 and w1. In each boundary, u0 or w0 gives the first boundary face and u1 or w1 gives the second. The directions of the corresponding alpha and beta curves are illustrated below.
As a final illustration, the example below shows the central surface in the case (n, k) = (9, 2).
regina::NTxIDiagonalCore::NTxIDiagonalCore | ( | unsigned long | newSize, | |
unsigned long | newK | |||
) |
Creates a new T x I
triangulation with the given parameters.
newSize | the number of tetrahedra in this triangulation. This must be at least 6. | |
newK | the additional parameter k as described in the class notes. This must be between 1 and (newSize - 5) inclusive. |
unsigned long regina::NTxIDiagonalCore::size | ( | ) | const [inline] |
Returns the total number of tetrahedra in this T x I
triangulation.
unsigned long regina::NTxIDiagonalCore::k | ( | ) | const [inline] |
Returns the additional parameter k as described in the class notes.
std::ostream & regina::NTxIDiagonalCore::writeName | ( | std::ostream & | out | ) | const [inline, virtual] |
Writes the name of this specific triangulation of T x I
to the given output stream.
The name will be written as a human-readable string.
out | the output stream to which to write. |
Implements regina::NTxICore.
std::ostream & regina::NTxIDiagonalCore::writeTeXName | ( | std::ostream & | out | ) | const [inline, virtual] |
Writes the name of this specific triangulation of T x I
in TeX format to the given output stream.
No leading or trailing dollar signs will be written.
out | the output stream to which to write. |
Implements regina::NTxICore.