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arXiv 0710.4532math-phhep-thmath.MP
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关于微分方程组的action原理

On the action principle for a system of differential equations

D. M. Gitman, V. G. Kupriyanov

摘要:

我们考虑的问题,构造一个作用泛函的物理系统的经典运动方程不能直接识别的欧拉-拉格朗日方程的作用原理。提出了作用原理构造的两种方式。从简单的考虑出发,我们得到了存在一个乘子矩阵的充要条件,该乘子矩阵能使一组给定的二阶微分方程具有Euler-Lagrange方程的结构.如果存在这样的乘数,则构造动作的显式形式。如果一个给定的微分方程组不能从作用量原理导出,人们可以用等价的一阶形式重新表述这样一个方程组,它总是可以被视为某个作用量的欧拉-拉格朗日方程。我们明确地构造这样一个动作。在将拉格朗日函数与给定的一组方程联系起来时,存在着一种模糊性(不简化为总时间导数)。我们提出了一个完整的描述这种模糊性。通过几个例子说明了一般程序。

英文摘要:

We consider the problem of constructing an action functional for physical systems whose classical equations of motion cannot be directly identified with Euler-Lagrange equations for an action principle. Two ways of action principle construction are presented. From simple consideration, we derive necessary and sufficient conditions for the existence of a multiplier matrix which can endow a prescribed set of second-order differential equations with the structure of Euler-Lagrange equations. An explicit form of the action is constructed in case if such a multiplier exists. If a given set of differential equations cannot be derived from an action principle, one can reformulate such a set in an equivalent first-order form which can always be treated as the Euler-Lagrange equations of a certain action. We construct such an action explicitly. There exists an ambiguity (not reduced to a total time derivative) in associating a Lagrange function with a given set of equations. We present a complete description of this ambiguity. The general procedure is illustrated by several examples.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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