释义 |
Beltrami IdentityAn identity in Calculus of Variations discovered in 1868 by Beltrami. The Euler-Lagrange DifferentialEquation is
 | (1) |
Now, examine the Derivative of 
 | (2) |
Solving for the term gives
 | (3) |
Now, multiplying (1) by gives
 | (4) |
Substituting (3) into (4) then gives
 | (5) |
 | (6) |
This form is especially useful if , since in that case
 | (7) |
which immediately gives
 | (8) |
where is a constant of integration.
The Beltrami identity greatly simplifies the solution for the minimal Area Surface of Revolution about a givenaxis between two specified points. It also allows straightforward solution of the Brachistochrone Problem. See also Brachistochrone Problem, Calculus of Variations, Euler-Lagrange Differential Equation,Surface of Revolution
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