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Oct.
2007
CHINESE
JOURNAL
OF
ENGINEERING
MATHEMATICS
Vo
l.
24
No.
5
Article
ID:
1005-3085 (2007) 05-0788-07
A
New
Nonmonotonic
Self-adaptive
Tr
ust
Region
AIgorithm
with
Line
Search*
YANG
Yang
1
,2,
SUN
Wen-yu
2
(1- School of Mathematics and Physics Science
,
Xl
时
10U
Institute of Technology, Xuzhou 221008;
2- School of Mathematics and Computer Science
, Nanjing Normal University, Nanjing 210097)
Abstract:
We propose a new
trust
region algorithm which
the
trust
region radius
is
updated
at
a
variable rate. Moreover
,
the
new algorithm performs a backtracking line search from the
fa
i!
ed point instead of resolving
the
trust
region subproblem. A nonmonotonic criterion
is
also used
to
speed up
the
convergence.
We
establish
the
global convergence of
the
new
algorithm. Numerical results are also presented.
Keywords:
unconstrained optimization;
trust
region; line search; nonmonotonic; global convergence
Classification:
AMS(2000) 90C30
CLC
number:
022
1.
2
Document
code:
A
1
Introduction
We
consider
the
following
unconstrained
optimization
problem
JEi:Lf(z)
,
、‘
1·''
咱
ai
''''-‘、、
where
f(x)
is twice
continuously
differentiable.
'fr
ust
region
method
is a
very
effective
and
robust
technique
for solving
problem
(1)
to
find
the
global
optimal
solution.
At
the
kth
step
,
it
calculates
a
trial
step
d
k
by
solving
the
following
trust
region
subproblem
,
d
Lκ
B
T
,
d
嘈
t--q
,"
十
,
G
TK
Qd
+
儿
U
=
<一
、}/
,
GHH
/l
飞
JU
ι
岛川川川
H
AV
n
.,
A4EU
mc
队
(2)
(3)
where
儿
f(Xk)
and
gk
V'
f(Xk)
are
the
function
value
and
the
gradient
vector
at
the
current
approximation
iterate
Xk
,
respectively
,
Bk
is
an
n x n
symmetric
matrix
which
may
be
the
exact
Hessian
H(Xk)
or
the
quasi-Newton
approximation
and
ßk
> 0 is
the
trust
region
radius.
In
this
paper
,
the
notation
11.11
denotes
the
Euclidean
norm
on
Rn.
After
obtaining
d
k
,
the
trust
region
method
computes
the
ratio
Tk
between
the
actual
reduction
and
the
predicted
reduction
of
the
objective
function
to
check
if
dk is
acceptable.
Then
the
trust
region
radius
ßk
is
also
updated
according
to
the
value
of
Tk
, since
Tk
reflect
the
extent
to
which
the
quadratic
Received
date:
2005-11-25.
Biography:
Yang Yang
(Born
in
1981)
,
Female
, Master,
Teachi
吨
Ass
istant. Research
field:
Nonlinear Programming.
*Foundation
item: The National Natural
Science
Foundation
of
China
(10231060)
, the Special Research
Fu
nd of Doctoral Program of Higher Education
of
China
(20040319003)
and the Graduates' Creative Project
of
Jiangsu Province, China
NO.
5
Yang
Yang
,
Sun
Wenyu:
Nonmonotonic Self-adaptive
τrust
Region
Algorithm with
Line
Search
789
model
如
(d)
approximates
the
objective
function f(Xk +
d).
Hei[lJ
proposed
a self-adaptive
trust
region
algorithm
,
in
which
ð.
k is
updated
by
R-function
at
a variable
rate.
Since
the
line search
strategy
and
the
trust
region
method
have
their
own
merits
, Nocedal
and
Yuan[2J suggested a
combination
of
the
trust
region
and
line
search
techniques.
Zhu[3J
also
proposed
a
method
to
combine
trust
region
and
line
search
techniques.
N
onmonotonic
line search
technique
for
unconstrained
optimization
is first
proposed
by
Grippo
et
a
l.
[4J.
Due
to
its
high efficiency,
many
authors
generalized
the
nonmonotonic
tech-
nique
to
trust
region
methods
and
proposed
nonmonotone
trust
region
methods
, see
[5
叫-
In
this
paper
, we will modify
and
improve
the
self-adaptive
trust
region
algorithm
proposed
in
[1
J
by
adopting
the
above
ideas:
backtracki
吨
line
search
and
nonmo
∞
tonic
technique.
In
the
next
section we discuss
our
new
algorithm.
In
section 3,
the
global convergence
property
of
the
new
algorithm
is established.
In
section 4,
the
results
of
numerical
experiments
are
reported.
2
Our
Algorithm
First
of
all, we
introduce
the
definition
of
the
R-function.
Definition
1
Any
one-dimensional
function
R
η
(t)
defined in R =
(一∞,+∞)
with
the
parameter
ηε(0
,
1) is
an
R-function
if
and
only if
it
satisfies:
1)
R,., (t) is non-decreasing in
(一∞,+∞);
2)
limt-+
一∞鸟
(t)
=
函,
whereβ1
巳
(0
,
1)
is a
small
constant;
3)
R,.,
(t)
三
1
一节,
for all t
<
ηwhereγ1ε(0
,
1
一
β1)
is a
constant;
4)
R
札
η)=1+
节,
whereγ2
E (0,
+∞)
is a
constant;
的
1imt
→+∞
R,.,
(t)
=
岛,
where
ß2
巳
(1
+币,+∞)
is a
constant
Fr
om
the
definition we
can
easily
get
the
following
important
properties
of
R-functions:
Theorem
2
An
R-function
R
札
t)
(where
ηε(0
,
1)) satisfies
0<β1
三
R,.,
(t)
三
1
一
γ1
< 1,
'V
t
ε(
一矶时,
1<1+γ2
三
Rη
(t)
三
β2<
十∞
,
'V
tE[
η
,+∞)
.
We
solve
the
subproblem
(2)-(3)
to
obtain
the
trial
step
d
k
satisfying
<<P
k
(0)
一
<<P
k(d
k
)
主
rllgkll
mi
叫ð.
k
,
llgkII/IIBkll}
and
d[gk
三
-rllgkll
min{
ð.
k, IIgkll/llBkll}
(4)
(5)
(6)
(7)
Relaxing
the
accepting
condition
on
d
k
, we use
the
nonmonotonic
trust
region technique.
Let
fl(k) = f(Xl(k)) =
^}l~aX"
,
f(Xk-j)
,
。三
3
三
m(k)
where
m(O)
= 0
and
m(k)
=
min{m(k
-1)
+ 1,
M}
,
and
M is a
nonnegative
integer.
Then
the
actual
reduction
of
f(x)
is defined
by
Aredk = fl(k) - f(Xk + dk)
and
the
predictive
reduction
of
f(x)
is Predk =
<<P
k(O)
一
<<P
k(dk).
Now
we give a
description
of
our
new
algorithm.
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