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单词 DerivationOfEulerLagrangeDifferentialEquationadvanced
释义

derivation of Euler-Lagrange differential equation (advanced)


Suppose that x0D. Choose r such that the closed ball of radius r about x0 is contained in D. Let q be any function whose support lies in this closed ball.

By the definition of F,

λF(q0+λq)=λDL(x,q0+λq,dq0+λdq)dmx
=λ(|x-x0|rL(x,q0+λq,dq0+λdq)dmx+xD|x-x0|>rL(x,q0+λq,dq0+λdq)dmx)

By the condition imposed on q, the derivative of the second integral is zero. Since the integrand of the first integral and its first derivativesMathworldPlanetmath are continuousMathworldPlanetmath and the closed ball is compact, the integrand and its first derivatives are uniformly continuous, so it is permissible to interchange differentiation and integration. Hence,

λF(q0+λq)=|x-x0|rL(x,q0+λq,dq0+λdq)λdmx
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更新时间:2025/5/5 5:25:43