• ʌ
Equate the last equations and use (23) and E = E = 0, then
~ ʌ '
ββ = _2»_ fc« _ (l±ni>∆k
=■ Φι(k)
C,0Λ^ s
is implied. ■
Proposition 7 The balanced accumulation function is a concave function with Φι(0)
= 0. Φι(∞) = _'x..Φ∣ (0) = ∞. Φ'ι(∞) = _«5,Φi(k)
and Φ1(k) < 0.
(≥ 0
I <0
for aka 1 {
≥ a5
< a5
ʌ
Proof. Rewrite (24) as Φ4(k) = α4 [k“ ± a5k] with a4 := Xq/cvqXv and a5 : =
(1 ± c∕s) Л/s, then Φχ(0) = 0. Φι(∞) = -∞. Differentiate Φ4(k) w.r.t. k, then
and therefore
Φ'1(k)
(≥0
I <0
for
aka 1
≥ α5
< a5
Iim Φ1 (k) = Iim (ak“ 1 — a5) = ∞
fc→0 fc→0 v ,
Iim Φ1(k) = Iim (ak“_ 1 — a5) = _a5.
fc→∞ fc→∞ `
Furthermore,
Φι(k) = (« _ 1) aa4k“-2 < 0
is implied. ■
Proposition 8 Suppose n — 2λ > 0. then < 0.
Proof. Take the derivative of (21) w.r.t. Λ and use n — 2Λ > 0, then
5Φι(k)
. . , , . . ʌ -,
(1 _ α)(1 _ £)(1 _ ω) Λo n _ 2Λ ± ɪkɑ"1
k“
ʌ
∂Λ
c 2 Г c , ,
cυ0λ n _ λ ± -ɪk" 1
is implied. ■
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