# Normal form (dynamical systems)

In mathematics, the normal form of a dynamical system is a simplified form that can be useful in determining the system's behavior.

Normal forms are often used for determining local bifurcations in a system. All systems exhibiting a certain type of bifurcation are locally (around the equilibrium) topologically equivalent to the normal form of the bifurcation. For example, the normal form of a saddle-node bifurcation is

${\displaystyle {\frac {\mathrm {d} x}{\mathrm {d} t}}=\mu +x^{2}}$

where ${\displaystyle \mu }$ is the bifurcation parameter. The transcritical bifurcation

${\displaystyle {\frac {\mathrm {d} x}{\mathrm {d} t}}=r\ln x+x-1}$

near ${\displaystyle x=1}$ can be converted to the normal form

${\displaystyle {\frac {\mathrm {d} u}{\mathrm {d} t}}=\mu u-u^{2}+O(u^{3})}$

with the transformation ${\displaystyle u=x-1,\mu =r+1}$.[1]

See also canonical form for use of the terms canonical form, normal form, or standard form more generally in mathematics.

## References

1. ^ Strogatz, Steven. "Nonlinear Dynamics and Chaos". Westview Press, 2001. p. 52.

## Further reading

• Guckenheimer, John; Holmes, Philip (1983), Nonlinear Oscillations, Dynamical Systems, and Bifurcations of Vector Fields, Springer, Section 3.3, ISBN 0-387-90819-6
• Kuznetsov, Yuri A. (1998), Elements of Applied Bifurcation Theory (Second ed.), Springer, Section 2.4, ISBN 0-387-98382-1
• Murdock, James (2006). "Normal forms". Scholarpedia. 1 (10): 1902. Bibcode:2006SchpJ...1.1902M. doi:10.4249/scholarpedia.1902.
• Murdock, James (2003). Normal Forms and Unfoldings for Local Dynamical Systems. Springer. ISBN 978-0-387-21785-7.