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单词 SymmetryOfASolutionOfAnOrdinaryDifferentialEquation
释义

symmetry of a solution of an ordinary differential equation


Let γ be a symmetry of the ordinary differential equationMathworldPlanetmath (http://planetmath.org/SymmetryOfAnOrdinaryDifferentialEquation) and x0 be a steady state solution of x˙=f(x). If

γx0=x0

then γ is called a symmetry of the solution of x0.

Let γ be a symmetry of the ordinary differential equation and x0(t) be a periodic solution of x˙=f(x). If

γx0(t-t0)=x0(t)

for a certain t0 then (γ,t0) is called a symmetry of the periodic solution of x0(t).

lemma: If γ is a symmetry of the ordinary differential equation and let x0(t) be a solution(either steady state or periodic) of x˙=f(x). Then γx0(t) is a solution of x˙=f(x).
proof: If x0(t) is a solution of dxdt=f(x) implies dx0(t)dt=f(x0(t)). Let’s now verify that γx0(t) is a solution, with a substitution into dxdt=f(x). The left hand side of the equation becomes dγx0(t)dt=γdx0(t)dt and the right hand side of the equation becomes f(γx0(t))=γf(x0(t)) since γ is a symmetry of the differential equation. Therefore we have that the left hand side equals the right hand side since dx0(t)dt=f(x0(t)).qed

References

  • GSS Golubitsky, Martin. Stewart, Ian. Schaeffer, G. David: Singularities and Groups in Bifurcation Theory (Volume II). Springer-Verlag, New York, 1988.
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更新时间:2025/5/5 0:24:42