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chordalTria -- makes a chordal network triangular

Synopsis

Description

This method puts a chordal network into triangular form. A triangular chordal network can be effectively used to compute several properties of the underlying variety.

Example 3.1 of [CP'17]

i1 : R = QQ[x_0..x_3, MonomialOrder=>Lex];
i2 : I = ideal {x_0^3-x_0, x_0*x_2-x_2, x_1-x_2, x_2^2-x_2, x_2*x_3^2-x_3};

o2 : Ideal of R
i3 : N = chordalNet I;
i4 : chordalTria N;
i5 : N

                         2
o5 = ChordalNet{ x  => {x  - 1, x , x  - 1} }
                  0      0       0   0
                 x  => {x , x  - 1}
                  1      1   1
                 x  => {x , x  - 1}
                  2      2   2
                 x  => {x , x  - 1}
                  3      3   3

o5 : ChordalNet

Example 1.3 of [CP'17]: ideal of adjacent minors of a 2xn matrix

i6 : I = adjacentMinorsIdeal(QQ,2,10);

o6 : Ideal of QQ[a..t]
i7 : N = chordalNet I;
i8 : chordalTria N;
i9 : N

o9 = ChordalNet{ a => { , a*d - b*c}                     }
                 b => { , b,  }
                 c => {c,  ,  , c*f - d*e}
                 d => {d, d,  ,  }
                 e => { ,  , e*h - f*g, e,  , e*h - f*g}
                 f => { , f,  , f,  ,  }
                 g => {g,  ,  , g*j - h*i,  , g*j - h*i}
                 h => {h, h,  ,  ,  ,  }
                 i => { ,  , i*l - j*k, i,  , i*l - j*k}
                 j => { , j,  , j,  ,  }
                 k => {k,  ,  , k*n - l*m,  , k*n - l*m}
                 l => {l, l,  ,  ,  ,  }
                 m => { ,  , m*p - n*o, m,  , m*p - n*o}
                 n => { , n,  , n,  ,  }
                 o => {o,  ,  , o*r - p*q,  , o*r - p*q}
                 p => {p, p,  ,  ,  ,  }
                 q => { ,  , q*t - r*s, q,  , q*t - r*s}
                 r => { , r,  , r,  ,  }
                 s => {s,  ,  ,  }
                 t => {t,  ,  }

o9 : ChordalNet

      

Caveat

This function calls triangularize, which is only implemented in Macaulay2 for binomial ideals. For arbitrary ideals we need to interface to Maple.

See also

Ways to use chordalTria :

For the programmer

The object chordalTria is a method function with options.