- #1
Whitehole
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- 4
Homework Statement
Consider the functional ##S(a,b) = \int_0^∞ r(1-b)a' \, dr ## of two functions ##a(r)## and ##b(r)## (with ##a' = \frac{da}{dr}##). Find the ##a(r)## and ##b(r)## that extremize ##S##, with boundary conditions ##a(∞) = b(∞) = 1##.
Homework Equations
The Attempt at a Solution
I know how to find ##b(r)##, my problem is ##a(r)##. This is what I've done,
##δS = \int_0^∞ r(1-η)a' \, dr = \int_0^∞ ra' \, dr + \int_0^∞ ra'η \, dr##
where ##η## is the variation in ##b##.
Can I say that since both terms should be ##0## so for the right term, since ##η## is arbitrary ##a' = 0## which implies the left term is also zero?