

Felix Sadyrbaev 


Leading
researcher, professor, Dr.habil.math. 
Leading
researcher, Dr.habil.math. 
Mathematical
Research Center, Department of Technology 
Laboratory
of Ordinary Differential Equations 
Institute of
Life Sciences and Technology 
Institute of Mathematics and Computer Science 
Daugavpils
University 
University of Latvia 
Parades street 1 
Raina bulvaris 29 
LV5400,
Daugavpils, Latvia 
LV1459, Riga, Latvia 
felix@latnet.lv 
felix@latnet.lv 


Research interests 

Research in
the theory of nonlinear boundary problems for ordinary differential
equations, theory of oscillations, asymmetric problems, qualitative
behavior of solutions of nonlinear differential equations, approximation
of solutions, calculus of variations, problems from applications, spectral
problems, analysis of three dimensional systems 
Education 


Dr.habil.math., University of Latvia, Riga, Latvia
Dissertation: Estimations of the number of solutions of nonlinear
boundary value problems.

Ph.D.
(Candidate of Science), Differential Equations, Belourussian State
University, Minsk
Dissertation: On some class of boundary value problems for a system of
the first order ordinary differential equations.
Advisor: Prof. Yurii
Klokov

Graduated
from Latvian State University, Faculty of Physics and Mathematics, Riga,
Latvia
Thesis: Properties of Operators in Hilbert Spaces.
Advised by Gennadiy Laptev

Teaching 

 Professor at the
Daugavpils University from 1999.
 Courses taught:
Basics of Optimization, Mathematical Modelling and Differential
Equations
 Coordinator of
Doctoral studies in Mathematics (Daugavpils University) from 2002

Research projects 


Fundamental and applied research project of the Latvian
Council of Science
"Analysis of complex dynamical systems in fluid
mechanics and heat transfer", Researcher, lzp2021/10076.

Latvian
Council of Science, Project Nr. 09.1220 Contemporary Methods of
Analyzing Dynamical Systems, Head of the project, 2009

Latvian
Council of Science, Project Nr. 05.1531 Nonlinear Boundary Value
Problems for Ordinary Differential Equations, Head of the project,
20052008.

Latvian
Council of Science, Project Nr. 01.0356 Nonlinear Boundary Value
Problems for Ordinary Differential Equations, Head of the project,
20012004.

Selected publications 




A. Gritsans, A. Kolyshkin, F. Sadyrbaev, and
I. Yermachenko, On the stability of a convective flow with nonlinear heat
sources,
Mathematics, 11(18): 3895, 2023.


A. Gritsans,
V. Koliskina, A. Kolyshkin, and F. Sadyrbaev, Linear stability of a
combined convective flow in an annulus,
Fluids,
8(4):130, 2023.

 A. Kirichuka and F. Sadyrbaev,
Boundary value problems for Liénardtype equations with quadratic
dependence on the "velocity", Abstract
and Applied Analysis, Vol. 2022 (2022), Article ID 9228511,
12 pages.



 I. Samuilik, F. Sadyrbaev, and D.
Ogorelova, Mathematical modeling of three  dimensional genetic
regulatory networks using logistic and Gompertz functions,
WSEAS Transactions on Systems and Control, Vol. 17, 2022, pp.
101107.



A. Kirichuka, F. Sadyrbaev, On the number of
solutions for a certain class of nonlinear secondorder boundaryvalue
problems,
Journal of Mathematical Sciences, Vol. 257, 2021, pp. 31–40.


D.A. Ogorelova, F.Zh. Sadyrbaev, Gompertz
function in the model of gene regulatory networks, Proceedings of the
International Conference on Mathematical Modelling in Applied Sciences —
ICMMAS'19. Belgorod, August 20–24, 2019,
Itogi Nauki i Tekhniki. Ser. Sovrem. Mat. Pril. Temat. Obz., Vol. 195,
VINITI, Moscow, 2021, pp. 88–96.


A. Gritsans,
V. Koliskina, A. Kolyshkin, and F. Sadyrbaev, On the stability of a
steady convective flow in a vertical layer of a chemically reacting
fluid, in: 9th edition of the International Conference on Computational
Methods for Coupled Problems in Science and Engineering (COUPLED
PROBLEMS 2021), Vol. IS34  Multiphysics Problems, 2021, 10
pp.


A. Gritsans,
A. Kolyshkin, D. Ogorelova,
F. Sadyrbaev, I. Samuilik, and
I. Yermachenko,
Solutions of nonlinear boundary value problem with applications to
biomass thermal conversion,
Proceedings of 20th International Scientific Conference "Engineering for
rural development" (May 2628, Jelgava, Latvia), 2021, pp.
837842.






 F. Sadyrbaev and S. Atslega, A remark
on attracting sets in genetic regulatory networks,
AIP Conference Proceedings, Vol. 2293, 090004, 2020.

 S. Atslega and F. Sadyrbaev, On modelling of artificial networks arising in applications, Proceedings of
19th International Scientific Conference
Engineering for Rural Development (May 2022, 2020, Jelgava,
Latvia), 2020, 19, pp. 16591665.

 F. Sadyrbaev, S. Atslega, and E.
Brokan, Dynamical Models of Interrelation in a Class of Artificial
Networks. In: Pinelas S., Graef J.R., Hilger S., Kloeden P., Schinas C.
(eds) Differential and Difference Equations with Applications. ICDDEA
2019. Springer Proceedings in Mathematics & Statistics, Vol. 333.
Springer, Cham, 2020.
https://doi.org/10.1007/9783030563233_18

 D. Ogorelova, F. Sadyrbaev, and V.
Sengileyev, Control in inhibitory genetic regulatory network models,
Contemporary Mathematics, Vol. 1, No. 5, 2020, pp. 421428.


E. Brokan and
F. Sadyrbaev,
Remarks on GRNtype
systems,
4open, Vol. 3, No. 8, 2020.



 A.V. Kirichuka and F.Zh. Sadyrbaev,
On the number of solutions for a certain class of nonlinear secondorder
boundaryvalue problems, Proceedings
of the International Conference on Mathematical Modelling in Applied Sciences
ICMMAS17, St. Petersburg Polytechnic University, July 2428, 2017,
Itogi Nauki i Tekhniki. Ser. Sovrem. Mat. Pril. Temat. Obz., 160, VINITI,
Moscow, 2019, pp. 32–41.

 F. Sadyrbaev and E. Brokan, On
controllability of nonlinear dynamical network,
AIP Conference Proceedings, Vol. 2116, Issue 1, 040005, 2019.


A. Kirichuka and
F. Sadyrbaev,
On boundary value
problem for equations with cubic nonlinearity and stepwise coefficient,
Differential Equations & Applications, Vol. 10, No. 4, 2018, pp.
433447.




 F. Sadyrbaev, On attracting sets in
artificial networks: cross activation,
ITM Web Conf., Vol. 16, Article Number 01005, 2018, 3. pp.


N. Sveikate and F.
Sadyrbaev, On conversion of resonant problem to nonresonant one,
Miskolc Mathematical Notes, Vol. 18, No. 2, 2017, 10591071.


E. Brokan and F. Sadyrbaev,
Attraction in network describing systems, Proceedings of the 17th
International Conference on Computational and Mathematical Methods in
Science and Engineering (Costa Ballena, Rota, Cadiz, Spain, 48 July,
2017), 2017, 415418.
CMMSE 2017


F. Sadyrbaev.
Note on resonant problems, Proceedings of the 17th International
Conference on Computational and Mathematical Methods in Science and
Engineering (Costa Ballena, Rota, Cadiz, Spain, 48 July, 2017), 2017,
18621864.
CMMSE 2017


E. Brokan and F. Sadyrbaev.
On attractors in gene regulatory
systems. American
Institute of Physics Conference Proceedings, 2017,
Vol. 1809, 020010.
American Institute of Physics


A. Gritsans,
F. Sadyrbaev,
and I. Yermachenko.
Dirichlet
boundary value problem for the second order asymptotically linear system. International
Journal of Differential Equations, Vol. 2016
(2016), Article ID 5676217, 12
pp. http://dx.doi.org/10.1155/2016/5676217.
Hindawi


D. Finaskins, E. Brokan, and F. Sadyrbaev.
Attracting sets in network regulatory theory. 2016 Advances in Wireless
and Optical Communications (RTUWO), 2016, 211  215.
IEEE Xplore



M. Dobkevich
and F. Sadyrbaev.
On different type solutions of boundary value problems.
Math. Modelling and Analysis,
Vol. 21, No. 5, 2016, 659667.



S. Atslega
and F. Sadyrbaev. Solutions of twopoint boundary value problems via
phaseplane analysis. E. J. Qualitative Theory of
Diff. Equ., Proc. 10'th Coll. Qualitative Theory of Diff. Equ., No. 4,
2016,
110.
EJQTDE


F. Sadyrbaev.
Oscillatory solutions of boundary value problems.
In:
Springer Proceedings in Mathematics & Statistics,
Vol. 164,
S. Pinelas, Z. Dosla, O. Dosly, P.E. Kloeden (Eds.),
Differential &
Difference Equations and Applications,
2016,
109117.
Springer


A. Gritsans
and F. Sadyrbaev.
The Nehari solutions and asymmetric minimizers, in: Proceedings
of the 10th AIMS Conference on
Dynamical Systems, Differential Equations and Applications
(Madrid, Spain, July 711, 2014), Discrete and Continuous Dynamical
Systems,
2015,
Suppl.,
562568.
American Institute of Mathematical Sciences


M. Dobkevich
and F. Sadyrbaev.
Types and multiplicity
of solutions to Sturm–Liouville boundary value problem. Math. Modelling and Analysis,
Vol. 20, No. 1, 2015, 18.


A. Kirichuka
and F. Sadyrbaev.
Multiple positive
solutions for the Dirichlet boundary value problems by phase plane
analysis. Abstract
and Applied Analysis,
Vol. 2015 (2015), Article ID 302185, 6
pages doi:10.1155/2015/302185.
Hindawi



E. Brokan and F. Sadyrbaev. Attracting Sets
in Gene Regulatory Systems. In Proceedings of International Conference on
Simulation, Modelling and Mathematical Statistics (SMMS 2015), 2015,
135138.
Link



M. Dobkevich, F.
Sadyrbaev, N. Sveikate,
and
I. Yermachenko. On types of solutions of the
second order nonlinear boundary value problems. Abstract
and Applied Analysis, Vol. 2014 (2014), Article ID 594931,
9 pages, http://dx.doi.org/10.1155/2014/594931.
Hindawi


A. Gritsans
and F. Sadyrbaev.
Unexpected solutions of the Nehari problem. International
Journal of Analysis,
Vol. 2014 (2014), Article ID 467831, 5
pages doi:10.1155/2014/467831.
Hindawi
pdf


N. Sveikate
and F. Sadyrbaev.
Quasilinearization for resonant boundaryvalue problems with mixed
boundary conditions, Nonlinear Oscillations,
Vol. 17, No. 1, 2014, 112126.
Nonlinear Oscillations
N. Sveikate
and F. Sadyrbaev.
Quasilinearization for resonant boundaryvalue problems with mixed
boundary conditions, Journal of Mathematical Sciences, Vol. 205, No. 6,
2015, 832847.
Springer


I. Yermachenko
and F. Sadyrbaev.
Quasilinearization and multiple solutions of the second order nonlinear
boundary value problem, Journal of Control Engineering and Technology,
Vol. 4, No. 1, 2014, 18.
EBSCO pdf



F. Sadyrbaev.
Twodimensional systems with
asymmetric principal part. In:
Springer Proceedings in Mathematics & Statistics,
Vol. 47,
S. Pinelas, M. Chipot, Z. Dosla (Eds.),
Contributions from the International Conference on Differential &
Difference Equations and Applications,
2013,
99111.
Springer



A. Gritsans
and F. Sadyrbaev.
Boundary value
problems for a supersublinear asymmetric oscillator: exact number of
solutions. International
Journal of Mathematics and Mathematical Sciences,
Vol. 2013 (2013), Article ID 705984, 9
pages doi:10.1155/2013/705984.
Hindawi
pdf


I. Yermachenko
and F. Sadyrbaev.
Quasilinearization technique for ΦLaplacian type equations. International
Journal of Mathematics and Mathematical Sciences,
Vol. 2012 (2012), Article ID 975760, 11 pages
doi:10.1155/2012/975760.
Hindawi


 Y.
Kozmina and
F.
Sadyrbaev.
On a
maximal
number
of period
annuli,
Abstract and Applied Analysis, Vol. 2011 (2011), Article ID 393875,
8 pages, doi:10.1155/2011/393875.
Hindawi



F. Sadyrbaev
and
N. Sergejeva.
On a
Fučik type spectral problem for the second order nonlinear differential
equation with the integral boundary condition.
Communications in Applied Analysis,
Vol. 15, No.
24, 2011,
557567.
Dynamic Publishers
pdf


S. Atslega
and F. Sadyrbaev. Multiple period annuli in Lienard
type equations. Applied Mathematics Letters, Vol. 23, No. 2, 2010,
165–169.
Elsevier


 M. Dobkevich and F. Sadyrbaev. Types
of solutions and approximation of solutions of second order nonlinear
boundary value problems. In: Amer. Inst. Phys. Conference Proceedings
Volume 1168, 260 – 263. Numerical Analysis and applied mathematics: International
Conference on Numerical Analysis and Applied Mathematics 2009:
Part 2, Rethymno, Crete (Greece), 18 – 22 September 2009.
American Institute of Physics


S. Atslega and F. Sadyrbaev. Multiple
positive solutions in the second order autonomous nonlinear boundary
value problems. In: American Institute of Physics Conference Proceedings
Vol. 1168, 873876. Numerical Analysis and Applied Mathematics: International
Conference on Numerical Analysis and Applied Mathematics 2009,
Part 1, Rethymno, Crete (Greece), 18 – 22 September 2009.
American Institute of Physics

 S. Atslega and F. Sadyrbaev. Multiple
solutions of the second order nonlinear Neumann BVP. Dynamics of
Continuous, Discrete and Impulsive Systems (Series A). DCDIS A
Supplement dedicated to the 6th International Conference on Differential
Equations and Dynamical Systems held in Baltimore, U.S.A., May 22  26 
Watam Press, 2009, 100–103.


A. Gritsans, F. Sadyrbaev,
and N. Sergejeva. Two parameter nonlinear eigenvalue problems.
Mathematical Models in Engineering, Biology, and Medicine, Proceedings of
the International Conference on Boundary Value Problems,
American Institute of Physics Conference Proceedings, 2009,
Vol. 1124, 185194.
American Institute of Physics


S. Atslega and F. Sadyrbaev. Period
annuli and multiple solutions for twopoint BVP. Tatra Mountains
Mathematical Publications, Vol. 43, 2009, 11–23.
Link



I. Yermachenko and F. Sadyrbaev.
Multiple solutions of nonlinear boundary value problems for
twodimensional differential systems. Dynamical Systems and Differential
Equations. Proc. of the 7th AIMS International Conference (Arlington,
TX, USA, 2008), DCDS Supplement 2009, 659  668.
American Institute of Mathematical Sciences

 F. Sadyrbaev and
I. Yermachenko.
Multiple solutions of twopoint nonlinear boundary value problems.
Nonlinear Analysis: TMA, Vol. 71, No. 12, 2009, e176 – e185, Proc.
WCNA 2008, Orlando FL, USA, 2008.
Elsevier



A. Gritsans
and F. Sadyrbaev.
Twoparametric nonlinear eigenvalue problems. E. J. Qualitative Theory of
Diff. Equ., Proc. 8'th Coll. Qualitative Theory of Diff. Equ., No. 10, 2008,
114.
EJQTDE


F. Sadyrbaev and
I. Yermachenko. Types
of solutions and multiplicity results for twopoint nonlinear boundary
value problems. Proceedings of AIMS' Sixth International Conference on
Dyn. Systems, Diff. Equations and Applications
University of Poitiers, Poitiers,
France, June 25  28, 2006, Discrete and Continuous Dynamical Systems 
Supplement 2007, American Institute of Mathematical Sciences,
10611069.
American Institute of Mathematical Sciences


 F. Sadyrbaev.
Multiplicity of solutions for second order twopoint boundary value
problems with asymptotically asymmetric nonlinearities at resonance.
Georgian Mathematical Journal, Vol. 14, No. 2,
2007, 351–360.
De Gruyter


A. Gritsans
and F. Sadyrbaev. On the Nehari solutions. Proceedings of Equadiff 11, International Conference on Differential Equations. CzechoSlovak
series, Bratislava, July 2529, 2005. [Part 2] Minisymposia and
contributed talks. Comenius University Press, Bratislava, 2007, pp.
437446.
Czech
Digital Mathematics Library


 A. Gritsans and F. Sadyrbaev, On sine
and cosine type functions, arising in the theory of nonlinear
differential equations, Acta Societatis Mathematicae Latviensis, no. 7,
Abstracts of the 6th Latvian Matematical Conference (April 78, 2006,
Liepaja, Latvia), Liepaja, p. 28, 2006.
pdf


 F. Sadyrbaev and
I. Yermachenko. Types
of solutions and multiplicity results for twopoint nonlinear boundary
value problems. Nonlinear Analysis: TMA, Vol. 63, No. 57, 2005,
e1725 – e1735.
Elsevier


A. Gritsans
and F. Sadyrbaev.
Characteristic
numbers of nonautonomous EmdenFowler type equations. Proceedings: 10th
International Conference "Mathematical Modelling and Analysis 2005'' and
2nd International Conference "Computational Methods in Applied
Mathematics'', 403408, Technika, Vilnius, 2005.
pdf


A. Gritsans
and F. Sadyrbaev.
Remarks on lemniscatic functions. Acta
Universitatis Latviensis, Vol. 688. Mathematics, 2005, 3950.
pdf
dspace.lu.lv


 F. Sadyrbaev. Nonlinear boundary value
problems of the calculus of variations. Discrete and Continuous
Dynamical Systems  Supplement Volume, American Institute of
Mathematical Sciences, 2003, 770779.
American Institute of Mathematical Sciences

 Yu. Klokov and F. Sadyrbaev. Sharp
conditions for rapid nonlinear oscillations. Nonlinear Analysis: TMA, Vol.
39, No. 39, 2000, 519–533.
Elsevier

 Yu. Klokov and F. Sadyrbaev. Rapid
oscillations in sublinear problems. Funkcialaj Ekvacioj, Vol. 42, No. 3,
1999, 339–353.
Link

 M. Henrard and F. Sadyrbaev.
Multiplicity results for fourthorder twopoint boundary value problems
with asymmetric nonlinearities. Nonlinear Analysis: TMA, Vol. 33, No. 3,
1998, 281–302.
Elsevier

 F. Sadyrbaev. Multiplicity of
solutions for twopoint boundary value problems with asymptotically
asymmetric nonlinearities, Nonlinear Analysis: TMA, Vol. 27, No. 9, 1996,
9991012.
Elsevier

 F. Sadyrbaev. Nonlinear twopoint
fourth order boundary value problems. Rocky Mountain Journal of
Mathematics, Vol. 25, No. 2, 1995, 757–781.
Link

Recent Conferences and Invited Talks 

 F. Sadyrbaev. Oscillations in
dynamical models of genetic networks (Plenary lecture, Online). The
International Conference: Dynamical Systems, Modeling, and Mathematical
Sciences. Dubai/UAE, September 2325, 2022.
https://dynamicalsystemsandmodeling.wordpress.com/

 F. Sadyrbaev. Creating periodic
attractors for dynamical systems modelling genetic networks.
International Conference „Computational and Mathematical Methods in
Science and Engineering,” Costa Ballena, Cádiz, Spain, July 3 – 8, 2022.

 F. Sadyrbaev. "From Duffing equation
to biooscillations". The International Conference „Conference on
Mathematical Analysis and Applications in Science and Engineering” ISEP
 Instituto Superior de Engenharia do Porto (ipp.pt), Porto, Portugal,
June 2729, 2022.

 F. Sadyrbaev, S. Atslega and E. Brokan.
On controllability of gene regulatory networks. 9th Internat. Congress
Industr. Appl. Mathematics (ICIAM), Valencia, Spain, July 1519, 2019.

 F. Sadyrbaev, S. Atslega and E. Brokan.
Dynamical models of interrelation in a class of artificial networks
(Invited lecture). International Conference on Differential & Difference
Equations and Applications 2019, (ICDDEA), Lisbon, Portugal, July 15,
2019.

 F. Sadyrbaev, S. Atslega and E. Brokan.
Attraction in gene regulatory systems. Short communication, Intern.
Congress Mathematicians 2018 (ICM 2018), Rio de Janeiro, 1–9 August 2018.

 F. Sadyrbaev, S. Atslega and E. Brokan.
Modelling artificial networks. ICM2018 Satellite event International
Conference on Industrial Mathematics  ICIM2018, Foz do Iguasu, Brasil,
23–27 July 2018.

 F. Sadyrbaev, E. Brokan. On solutions
of a system of ordinary differential equations arising in applications.
12th American Inst. Math. Studies Conference on Dynamical Systems
(AIMS), Differential Equations and Applications, Taipei, Taiwan, July 5
 July 9, 2018.


International conference of numerical analysis and applied
mathematics (ICNAAM2016), Rhodes, Greece, 2016.
http://icnaam.org/




The 2015 International Conference on Simulation, Modelling and
Mathematical Statistics, Chiang Mai,
Thailand.
http://www.smms2015.org/




The international
conference "Actual problems of mathematics and mathematical modeling",
dedicated to the 50th anniversary of the foundation of the Institute of
Mathematics and Mathematical Modeling of Education and Science Ministry
of the Republic of Kazakhstan, in Almaty, 2015.
http://www.math.kz/conf/index.php/en/





Symposium on Differential Equations and Difference Equations,
Homburg/Saar, Germany,
2014.



F. Sadyrbaev, A. Gritsans. On extension of NehariMoore
example//Book of abstracts of Conference on Differential and Difference
Equations and Applications, Jasná, Slovak Republic, June 2327, 2014, P.
49.
http://fpv.uniza.sk/cddea2014/


Symposium on Differential Equations and Difference Equations SDEDE 2013,
Bayrischzell, Germany,
2013.


 International Conference on the
Theory, Methods and Applications of Nonlinear Equations,
Kingsville,
USA, 2012.
Link

 Symposium on differential equations
and difference equations,
Novacella,
Italy, 2012.
Link

 The Fifth International Workshop
Constructive methods for nonlinear boundary value problems,
Tokaj,
Hungary, 2012.
Link

 7th European Conference on Elliptic
and Parabolic Problems,
Gaeta,
Italy, 2012.
Link

 Equadiff,
Loughborough University, GB,
2011.
Link

 International Conference on
Differential & Difference Equations,Ponta
Delgada, Portugal, 2011.
Link

 General Assembly of International
Mathematical Union, Bangalore, India, 2010.
Link

 The 8th AIMS Conference on Dynamical
Systems, Differential Equations and Applications, Dresden, Germany, 2010.
Link

 Emerging Problems in Nonlinear
Analysis and Differential Equations: Advances in Theory and
Applications, Glasgow, 2010.
Link

 Conference on Differential and
Difference Equations and Applications 2010 (CDDEA 2010), Rajecke Teplice,
Slovakia (invited lecturer and member of program committee).
Link

 7th ISAAC Congress, Imperial College,
London, 2009.
Link

 World Congress of Nonlinear Analysts
2008, FL, USA, July 2008, Orlando, FL, USA (invited lecturer in two
special sessions).
Link

 Conference on Boundary Value Problems
Mathematical Models In Engineering, Biology And Medicine, September
1619, 2008, Santiago de Compostela, Spain (invited lecturer).
Link

 Conference on Differential and
Difference Equations and Applications, Strečno, Slovak
Republik, 2008 (invited lecturer and member of
program committee).
Link

 The 6th International Conference On
Differential Equations and Dynamical Systems, May 2226, 2008,
Baltimore,
Maryland, USA.
Link

 Amer. Inst. Math. Stud. 7th
International Conference on Dyn. Systems, Diff. Equations and
Applications, University of Texas at Arlington, Texas, USA May 18
 21, 2008.
Link

 Equadiff07, Vienna, Austria, 2007.
Link

 Amer. Inst. Math. Stud. 6th
International Conference on Dyn. Systems, Diff. Equations and
Applications, University of Poitiers, Poitiers, France, June 25 
28, 2006.
Link


The World Congress of Nonlinear Analysts
2004, FL, USA, July 2004, Orlando, FL, USA (invited lecturer in two
special sessions).
Link

 Equadiff2003, July 2226, 2003,
Hasselt, Belgium.
Link

 International Congress of
Mathematicians, Bejing, China, 2002.
Link

 Fourth International Conference on
Dynamical Systems and Differential Equations, May 24  27, 2002,
Wilmington, NC, USA (invited lecture).

Activities 

 Member of the Latvian
Mathematical Society
 Member of the American Mathematical
Society


