This project is a Singular library for computing with matrix factorisations, mathematical objects appearing in singularity theory and topological field theory. Features include:
- Computing Khovanov-Rozansky knot homology (
- Fusion of defects in Landau-Ginzburg models (
- Fusion of equivariant defects in Landau-Ginzburg models (
The code was written by Nils Carqueville and Daniel Murfet as part of the paper "Computing Khovanov-Rozansky homology and defect fusion". Other contributors are most welcome! If you have any questions, please don't hesitate to get in touch.
- 2/11/2020 - new fusion code (
blownew.lib) which computes Atiyah classes for arbitrary potentials without reduction to a system of parameters given by powers of ring variables (which was done in the old
blow.libcode). Based on this there is a new library
blowequiv.libfor fusing equivariant defects, see
- 16/10/2020 - code and examples checked against current version of Singular (4.1.0).
Installation & Usage
First you need a working installation of the commutative algebra package Singular. Singular is available for Linux, Windows and Mac OS X and is easy to install. Then you should either clone this git repository onto your local machine, or download it as a ZIP file.
From within the folder containing this repository, run
Singular. You will see a welcome screen like this:
SINGULAR / A Computer Algebra System for Polynomial Computations / version 4.0.1 0< by: W. Decker, G.-M. Greuel, G. Pfister, H. Schoenemann \ Sep 2014 FB Mathematik der Universitaet, D-67653 Kaiserslautern \
At this point you can start cutting and pasting into the Singular shell from the files in the folder
examples of this repository. In
examples/blow-example.txt you will find examples relating to defect fusion (i.e. functors between categories of matrix factorisations) while in
examples/linkhom-example.txt you will find examples of Khovanov-Rozansky homology calculations.
Here is an extract from
examples.txt which shows the canonical way to compute fusions using the library:
//////////////////////////////////////////////// // Example of defect fusion using webCompilePair //////////////////////////////////////////////// // For the fusion of defects with boundary conditions, or defect-defect fusion // (i.e. convolution of matrix factorisation "kernels") we use webCompilePair, // which takes as input an oriented graph (called a "web") whose edges are // decorated with potentials (i.e. the equation of an isolated singularity) and // whose vertices are decorated with matrix factorisations. The output is a finite // rank matrix factorisation homotopy equivalent to the "total factorisation" of // the web. All these terms are defined more precisely in the preamble of mfweb.lib // and the paper arXiv: 1108.1081, but let us proceed to the example. // // The web has two vertices (marked with X,Y) and two edges (marked x^3, y^5) // // X ---- x^3 ----> Y ---- y^5 ----> // // Here the second edge (labelled with y^5) goes to the boundary. // // For this to be a valid web, Y needs to be a matrix factorisation of y^5 - x^3 // (i.e. outgoing potential minus incoming potential) while X needs to be a matrix // factorisation of x^3. The total factorisation is Y \otimes X, as a matrix // factorisation of y^5 over the variables y. This is infinite rank but is // homotopy equivalent to a finite rank matrix factorisation. // // This finite rank matrix factorisation is, by definition, the image of // X \in hmf(x^3) under the functor hmf(x^3) --> hmf(y^5) induced // by the kernel Y. Let us compute this finite rank guy now. Then we will move // onto more complicated examples. option(noredefine);option(noloadLib);option(redSB); LIB "mfweb.lib"; ring rr=0,(x,y),dp; // We encode the web given above as a pair of edges, and a pair of vertices. // Format for an edge is (source, target, variable, potential). Start indexing // your vertices at 1, since 0 stands for the boundary. list e1 = list(1,2,list(x),x^3); list e2 = list(2,0,list(y),y^5); list edgeList = list(e1,e2); // Now define the mfs X,Y to be placed at each vertex matrix X = 0, x^2, x, 0; matrix Y0 = -x, y, -y^4, x^2; matrix Y1 = x^2, -y, y^4, -x; matrix z; matrix Y = blockmat(z,Y1,Y0,z); list mfs = X, Y; // Define the web list web = list(2, edgeList, mfs); // 2 for the number of vertices webVerify(web); // The compilation of this web is the fusion of Y with X. list compStrat = defaultCompStratForWeb(web); list L = webCompilePair(web, compStrat); print(L); // The answer is a direct sum of two copies of the Koszul factorisation (y,y^4)
For an explanation of the mathematics behind this code, see Dyckerhoff-Murfet and Murfet. There is also extensive documentation within the libraries themselves, see