This package is a collection of Fortran 90 subroutines for accurately and efficiently solving matrix eigenvalue problems using essentially 2x2 unitary matrices.

• Jared L. Aurentz, University of Oxford, United Kingdom
• Thomas Mach, KU Leuven, Belgium
• Raf Vandebril, KU Leuven, Belgium
• David S. Watkins, Washington State University, United States

To get started with eiscor please checkout the [guide] (https://github.com/eiscor/eiscor/blob/master/docs/GUIDE.md).

This software is based on the following articles:

1. Jared L. Aurentz, Thomas Mach, Raf Vandebril, and David S. Watkins. [Fast and stable unitary QR algorithm.] (http://etna.mcs.kent.edu/volumes/2011-2020/vol44/abstract.php?vol=44&pages=327-341) Electronic Transactions on Numerical Analysis. Vol. 44, pp. 327-341. 2015.
2. Jared L. Aurentz, Thomas Mach, Raf Vandebril, and David S. Watkins. [Fast and backward stable computation of roots of polynomials.] (http://epubs.siam.org/doi/10.1137/140983434) SIAM Journal on Matrix Analysis and Applications. Vol. 36, No. 3, pp. 942-973. 2015.
3. Thomas Mach and Raf Vandebril. [On deflations in extended QR Algorithms.] (http://epubs.siam.org/doi/abs/10.1137/130935665) SIAM Journal on Matrix Analysis and Applications. Vol. 35, No. 2, pp. 559–579. 2014.
4. Raf Vandebril and David S. Watkins. An extension of the QZ algorithm beyond the Hessenberg-upper triangular pencil. Electronic Transactions on Numerical Analysis. Vol. 40, pp. 17-35. 2013.
5. Raf Vandebril and David S. Watkins. A generalization of the multishift QR-algorithm. SIAM Journal on Matrix Analysis and Applications. Vol. 33, No. 3, pp. 759-779. 2012.
6. Raf Vandebril. Chasing bulges or rotations? A metamorphosis of the QR-algorithm. SIAM Journal on Matrix Analysis and Applications. Vol. 32, No. 1, pp. 217-247. 2011.