Fuchs' theorem

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In mathematics, Fuchs' theorem, named after Lazarus Fuchs, states that a second order differential equation of the form

y'' + p(x)y'+q(x)y=g(x)\;

has a solution expressible by a generalised Frobenius series when p(x), q(x) and g(x) are analytic at x=a or a is a regular singular point. That is, any solution to this second order differential equation can be written as

 y = \sum_{n=0}^\infty a_n (x-a)^{n+s} , \quad a_0 \neq 0

for some real s, or

 y = y_0 \ln (x-a) + \sum_{n=0}^\infty b_n(x-a)^{n+r}, \quad b_0 \neq 0

for some real r, where y0 is a solution of the first kind.

Its radius of convergence is at least as large as the minimum of the radii of convergence of p(x), q(x) and g(x).

See also[edit]


  • Asmar, Nakhlé H. (2005), Partial differential equations with Fourier series and boundary value problems, Upper Saddle River, NJ: Pearson Prentice Hall, ISBN 0-13-148096-0 .
  • Butkov, Eugene (1995), Mathematical Physics, Reading, MA: Addison-Wesley, ISBN 0-201-00727-4 .