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.

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. 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. 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. 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.