1. Department of Applied Mathematics, Charles University, Malostranské nám. 25, 118 00 Praha 1, Czech Republic
2. Department of Applied Mathematics, Charles University, Malostranské nám. 25, 118 00 Praha 1, Czech Republic, and Department of Computer Science, ETH Zurich, 8092 Zurich, Switzerland
3. Instituto de Matemáticass, Unidad Juriquilla, Universidad Nacional Autónoma de México, Juriquilla Querétaro 76230, México
4. Department of Applied Mathematics and Computer Science Institute, Charles University, Malostranské nám. 25, 118 00 Praha 1, Czech Republic