randomRationalCurve -- creates the ideal of a random rational curve of degree (d,e) in P^1xP^2

Synopsis

Usage:

randomRationalCurve(d,e,F)

randomRationalCurve(d,e)
Inputs:
- d, an integer, degree of curve on the $\PP^1$ factor of $\PP^1\times\PP^2$
- e, an integer, degree of curve on the $\PP^2$ factor of $\PP^1\times\PP^2$
- F, a ring, base ring
Outputs:
- an ideal, defining random rational curve in $\PP^1\times\PP^2$ of degree (d,e) over F.

Description

Given two positive integers d,e and a ring F, randomRationalCurve returns the ideal of a random curve in $\PP^1\times\PP^2$ of degree (d,e) defined over the base ring F.

This is done by randomly generating two homogeneous polynomials of degree d and three homogeneous polynomials of degree three in $F[s,t]$ defining maps $\PP^1\to\PP^1$ and $\PP^1\to\PP^2$, respectively. The graph of the product of these two maps in $\PP^1\times(\PP^1\times\PP^2)$ is computed, from which a curve of bi-degree (d,e) in $\PP^1\times\PP^2$ over F is obtained by saturating and then eliminating.

If no base ring is specified, the computations are performed over ZZ/101.

i1 : randomRationalCurve(2,3,QQ);

o1 : Ideal of QQ[x   ..x   , x   ..x   ]
                  0,0   0,1   1,0   1,2

i2 : randomRationalCurve(2,3);

               ZZ
o2 : Ideal of ---[x   ..x   , x   ..x   ]
              101  0,0   0,1   1,0   1,2

Caveat

This creates a ring $F[x_{0,0},x_{0,1},x_{1,0},x_{1,1},x_{1,2}]$ in which the resulting ideal is defined.

Ways to use randomRationalCurve :

randomRationalCurve(ZZ,ZZ)
randomRationalCurve(ZZ,ZZ,Ring)

For the programmer

The object randomRationalCurve is a method function.