Multidisciplinary design optimization: Difference between revisions
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In [[complex analysis]], a '''zero''' (sometimes called a '''root''') of a [[holomorphic function]] ''f'' is a [[complex number]] ''a'' such that ''f''(''a'') = 0. | |||
==Multiplicity of a zero== | |||
A complex number ''a'' is a '''simple zero''' of ''f'', or a '''zero of multiplicity 1''' of ''f'', if ''f'' can be written as | |||
:<math>f(z)=(z-a)g(z)\,</math> | |||
where ''g'' is a [[holomorphic function]] ''g'' such that ''g''(''a'') is not zero. | |||
Generally, the '''[[multiplicity (mathematics)|multiplicity]]''' of the zero of ''f'' at ''a'' is the positive integer ''n'' for which there is a holomorphic function ''g'' such that | |||
:<math>f(z)=(z-a)^ng(z)\ \mbox{and}\ g(a)\neq 0.\,</math> | |||
The multiplicity of a zero ''a'' is also known as the '''order of vanishing''' of the function at ''a''. | |||
==Existence of zeros== | |||
The [[fundamental theorem of algebra]] says that every nonconstant [[polynomial]] with complex coefficients has at least one zero in the [[complex plane]]. This is in contrast to the situation with [[real number|real]] zeros: some polynomial functions with real coefficients have no real zeros. An example is ''f''(''x'') = ''x''<sup>2</sup> + 1. | |||
==Properties== | |||
An important property of the set of zeros of a holomorphic function of one variable (that is not identically zero) is that the zeros are isolated. In other words, for any zero of a holomorphic function there is a small disc around the zero which contains no other zeros. | |||
There are also some theorems in complex analysis which show the connections between the zeros of a holomorphic (or meromorphic) function and other properties of the function. In particular [[Jensen's formula]] and [[Weierstrass factorization theorem]] are results for complex functions which have no counterpart for functions of a real variable. | |||
==See also== | |||
* [[Root of a function]] | |||
* [[Pole (complex analysis)]] | |||
* [[Hurwitz's theorem (complex analysis)]] | |||
* [[Rouché's theorem]] | |||
* [[Filter design]] | |||
* [[Nyquist stability criterion]] in [[control theory]] | |||
* [[Marden's theorem]] | |||
* [[Sendov's conjecture]] | |||
* [[Gauss–Lucas theorem]] | |||
==References== | |||
*{{cite book |last=Conway |first=John |title=Functions of One Complex Variable I |year=1986 |publisher=Springer |isbn=0-387-90328-3}} | |||
*{{cite book |last=Conway |first=John |title=Functions of One Complex Variable II |year=1995 |publisher=Springer |isbn=0-387-94460-5}} | |||
== External links == | |||
* {{MathWorld | urlname= Root | title= Root}} | |||
* [http://math.fullerton.edu/mathews/c2003/SingularityZeroPoleMod.html Module for Zeros and Poles by John H. Mathews] | |||
* [http://directory.fsf.org/wiki/ZerSol Free C++ solver for zeros of an analytic function (with C and Fortran bindings) by Ivan B. Ivanov] | |||
[[Category:Complex analysis]] | |||
[[Category:Zero]] |
Revision as of 21:15, 8 January 2014
In complex analysis, a zero (sometimes called a root) of a holomorphic function f is a complex number a such that f(a) = 0.
Multiplicity of a zero
A complex number a is a simple zero of f, or a zero of multiplicity 1 of f, if f can be written as
where g is a holomorphic function g such that g(a) is not zero.
Generally, the multiplicity of the zero of f at a is the positive integer n for which there is a holomorphic function g such that
The multiplicity of a zero a is also known as the order of vanishing of the function at a.
Existence of zeros
The fundamental theorem of algebra says that every nonconstant polynomial with complex coefficients has at least one zero in the complex plane. This is in contrast to the situation with real zeros: some polynomial functions with real coefficients have no real zeros. An example is f(x) = x2 + 1.
Properties
An important property of the set of zeros of a holomorphic function of one variable (that is not identically zero) is that the zeros are isolated. In other words, for any zero of a holomorphic function there is a small disc around the zero which contains no other zeros. There are also some theorems in complex analysis which show the connections between the zeros of a holomorphic (or meromorphic) function and other properties of the function. In particular Jensen's formula and Weierstrass factorization theorem are results for complex functions which have no counterpart for functions of a real variable.
See also
- Root of a function
- Pole (complex analysis)
- Hurwitz's theorem (complex analysis)
- Rouché's theorem
- Filter design
- Nyquist stability criterion in control theory
- Marden's theorem
- Sendov's conjecture
- Gauss–Lucas theorem
References
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My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 - 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
External links
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