X.
Dai
et
al.
/
Applied
Soft
Computing
35
(2015)
541–557
543
It
means
that
the
new
harmony
with
better
state
will
replace
the
harmony
with
the
worst
fitness
value
in
HM.
Step
5:
Check
the
stopping
criterion.
If
the
stopping
criterion
is
met,
algorithm
computation
is
terminated.
Otherwise,
go
to
Step
3.
4.
The
proposed
SAMOHS
algorithm
When
the
HS
is
employed
to
solve
MOPs,
it
is
difficult
to
set
its
control
parameters.
On
one
hand,
the
performance
of
HS
is
extremely
sensitive
to
values
of
control
parameters.
This
means
that
different
parameter
values
can
cause
different
performance
in
terms
of
convergence
precision,
convergence
rate
and
reliabil-
ity.
On
the
other
hand,
the
fixed
parameter
value
is
inappropriate
for
balancing
diversity
and
intensity
during
the
search
process.
Although
various
dynamic
parameters
setting
strategies
and
self-
adaptive
mechanisms
have
been
proposed
for
single
objective
HS
algorithm,
there
are
few
researches
for
multi-objective
HS
algo-
rithm.
In
addition,
dynamic
parameters
setting
strategies
still
have
some
disadvantages
[12]
,
such
as
all
decision
variables
use
the
same
control
parameter
during
the
search
process.
This
is
difficult
to
find
a
good
balance
between
exploration
and
exploitation
since
each
decision
variable
has
its
own
characteristics.
In
view
of
these
problems,
a
novel
self-adaptive
mechanism
for
multi-objective
HS
algorithm
is
proposed
in
this
paper.
The
proposed
self-adaptive
mechanism
has
three
main
improvements,
including
(a)
each
decision
variable
has
its
own
control
parame-
ters,
which
are
updated
adaptively
during
the
search
process;
(b)
self-adaptive
parameter
setting
based
on
variation
of
HM
variance
is
employed
for
HMCR
and
PAR;
(c)
a
modified
self-adaptive
bw
is
proposed
for
HS.
The
details
of
the
proposed
SAMOHS
algorithm
are
described
below.
4.1.
Implementation
of
SAMOHS
In
this
section,
the
proposed
SAMOHS
based
on
HM
variance
is
presented.
It
should
be
noted
that
the
HM
updating
for
MOPs
is
different
from
single
objective
optimization.
For
the
HM
updat-
ing
in
solving
MOPs,
the
HM
is
updated
after
generating
HMS
new
harmonies
instead
of
one
harmony
at
each
iteration.
The
imple-
mentation
procedure
of
the
proposed
SAMOHS
is
shown
in
Fig.
1
and
it
can
be
summarized
as
follows:
Step
1.
Initialize
the
algorithm
parameters.
Set
the
maximal
number
of
iteration
T,
let
iteration
counter
t
=
1,
randomly
generate
initial
harmony
memory
HM
t
and
evaluate
all
harmonies
in
HM
t
.
Specify
the
minimum
value
and
maximum
value
as
HMCR
min
and
HMCR
max
,
set
[PAR
mean1
,
PAR
std1
]
and
[PAR
mean2
,
PAR
std2
]
for
PAR,
set
[K
min1
,
K
max1
]
and
[K
min1
,
K
max1
]
for
K
and
HMS.
Step
2.
Update
the
control
parameters.
The
control
parame-
ter
values
HMCR
j,t
,
PAR
j,t
and
bw
j,t
for
each
variable
are
assigned
according
to
the
proposed
self-adaptive
mechanism
as
described
in
Section
4.2.
Step
3.
Improvise
a
new
harmony
memory.
Execute
the
proce-
dure
of
improvisation
as
shown
in
Algorithm
1
by
using
parameter
values
HMCR
j,t
,
PAR
j,t
and
bw
j,t
for
HMS
times
to
form
a
new
har-
mony
memory
HM
new
t
.
Step
4.
Evaluate
fitness
value.
Evaluate
the
fitness
value
of
each
harmony
in
HM
new
t
.
Step
5.
Update
harmony
memory.
The
detailed
updating
proce-
dure
of
HM
is
described
in
Section
4.3.
Step
6.
Check
termination
criterion.
If
t
≥
T
is
reached,
set
A
to
the
set
of
solutions
expressed
by
the
non-dominated
solutions
in
HM
t+1
,
output
the
non-dominated
set
A
and
terminate
the
algo-
rithm.
Otherwise,
increase
iteration
counter
(t
=
t
+
1)
and
go
to
Step
2.
Start
Evaluate the fitness value for each harmony in
the new h
armony m
emory
t<T
End
Update the harmony memory
according to
non-
domin
ated sorting and truncating procedure
Improvise for HMS times to form a new
harmony
memor
y
Update control parameters according to the
proposed self-adaptive mechanism
Initialize SAMOHS algorithm control
parameters
N
Y
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Fig.
1.
The
implementation
procedure
of
the
proposed
SAMOHS
algorithm.
Fig.
2.
Variable
encoding
format.
4.2.
Novel
self-adaptive
mechanism
for
SAMOHS
Since
the
key
parameters
HMCR,
PAR
and
bw
play
a
crucial
role
on
the
performance
of
HS
algorithm
and
it
is
really
diffi-
cult
to
tune
these
parameters,
a
novel
self-adaptive
mechanism
based
on
the
variation
of
the
HM
variance
is
proposed
in
this
paper.
It
is
necessary
to
emphasize
that
the
proposed
self-adaptive
parameter
setting
is
inspired
by
single
objective
differential
evolution
algorithm
[22],
however
the
proposed
self-adaptive
parameter
setting
is
based
on
the
HM
variance.
The
details
of
the
proposed
self-adaptive
mechanism
for
SAMOHS
are
described
below.
Firstly,
HMCR
j,t
,
PAR
j,t
and
K
j,t
are
encoded
into
each
decision
variable
x
j
,
as
shown
in
Fig.
2.
Here
t
denotes
the
current
itera-
tion
and
K
j,t
is
a
mutative
coefficient
used
to
modify
the
distance
bandwidth
bw
j,t
.
Thereafter,
the
parameters
HMCR
j,t
,
PAR
j,t
and
K
j,t
are
adaptively
updated
as
follows
during
the
search
process.
If
the
variation
of
VAR
j
is
Case
1
or
Case
2,
HMCR
j,t
,
PAR
j,t
and
K
j,t
are
renewed
by
Eqs.
(8)–(10),
respectively.
Otherwise,
HMCR
j,t
,
PAR
j,t
and
K
j,t
are
all
renewed
by
Eq.
(5).
Here,
Case
1
is
defined
as:
the
HM
variance
value
VAR
j
of
jth
variable
decreases
in
˛
(˛
=
3
is
utilized
in
this
paper)
consecutive
iterations.
Case
2
is
defined
as:
the
HM