Homotopy Perturbation Method For A Seir Model With Varying Total Population Size

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HOMOTOPY PERTURBATION METHOD FOR A SEIR
MODEL WITH VARYING TOTAL POPULATION SIZE


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.Jaharuddin

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Bogor Agricultural University
Jalan Meranti, Kampus !PB Dramaga

Bogor 16680, Indonesia

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e-mail: jaharipb@yahoo.com
Abstract

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We consider a SElR model with varying total population size. We find
the analytical solution of the proposed model


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solution of the nonlinear problem. By using this 1ncthod, we solve the
problem analytically and then compare the nu1nerical result with other
standard 1nethods. We also justify the numerical simulation and their
results. The comparison reveals that our approximate solutions are in
very good agreement with those by numerical 1nethod. Moreover, the

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results show that the proposed method is a 1norc reliable, efficient and

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I. Introduction

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Mathematical modelling has become important tools in analyzing the
spread and control of infectious diseases. The model helps us to understand


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by homotopy

perturbation method which is one of the best 1nethods for finding the

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different factors such as the transmission and recovery rates and to predict
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Keywords and phrases: epidemic models, homotopy perturbation method, system of nonlinear
differential equation.

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188

Homotopy Perturbation Method for a SEIR Model ...

Jaharuddin


189

.: how the diseases will spread over a period of time I 11. In recent years, many

method, this method is independent of small parameters and can overcome

: aitcmpts have been made to develop realistic mathematical models for

the restrictions of the perturbation methods. The homotopy perturbation

' investigating the transmission dynamic of infectious diseases. One of them is

method provides a universal technique to introduce a perturbative parameter.

: a ·model of epidemic which is usually given as a system of differential

This method has been introduced in 1999 by He [6] and was further

equations. To understand the behavior of epidemic model, we need to know


developed and improved by him [4]. The method has been used by many

the analysis of steady state and their stability 18 I. Studies of epidemic models

authors [3] in a wide variety of scientific and engineering applications to

that incorporate disease caused death and varying total population have

solve different types of governing differential equations. In this paper, the

become one of the in1portant areas in the mathematical theory of

basic idea of the homotopy perturbation method is introduced and then, the

epidemiology. Most of the research literatures on these types of models

nonlinear equation of SE!R model is solved through the homotopy

assume that the disease incubation is negligible so that once infected, each


perturbation method. The purpose of this paper is to extend the homotopy

susceptible individual instantaneously becomes infected and later recovered

perturbation method for computing the approximate analytical solution of a

with a permanent or tcrnporary acquired immunity. A compartmental model

SEIR model with varying total population size and then see how these

based on these assumptions is customarily called a SIR model. Models that

solutions compare with the solutions by numerical method.

arc more general than the SIR types need to be studied to investigate the role

This paper is organized as follows: Sections 2 and 3 are devoted to a
short description of the SEIR models with varying total population size and
the analysis of homotopy perturbation method, respectively. In Section 4, we

present the analytical approximate solutions obtained by implementing the
homotopy perturbation method to the SEIR model with varying total

of incubation in disease transmission I 101. Using a compartmental approach,
one may assume that a susceptible individual first goes through a latent
period after infection before becoming infected. The resulting models are of
SE!R types depending on whether the acquired immunity is permanent or
otherwise. In this article, the SE!R model with varying total population size
will be discussed and this model is in the form of nonlinear.

population size followed by comparison of results between the approximate
solutions and the solutions obtained by numerical method. The last section is

conclusion.
We know that except a limited number of these problems, most of them
'do not have analytical solution. Therefore, these nonlinear equations should

2. Mathematical Formulation

be solved using other methods. Some of them arc solved using numerical

considered so as to avoid divergence or inappropriate result. In the analytical

Formulation of SE!R model with varying total population size using by a
compartmental approach is given by Li and Fang [7]. It is assumed that the

perturbation method, we should exert the small parameter in the equation.

local density of the total population is a constant. A population of size N(t)

Therefore, finding the small parameter and exerting it into the equation are
difficulties of this method. Many different mathematical methods have been

is partitioned into subclasses of individuals who are susceptible, exposed
(infected but not yet infectious), infectious and recovered, with sizes denoted

recently introduced to eliminate the small parameter. In 1992, Liao [9] has

by S(t), E(t), l(t), and R(t), respectively. The sum E(t) + l(t) is the total

proposed a new analytical method called the homotopy analysis method,

infected population. Our assumptions on the dynamical transfer of the
population are then demonstrated in the form of SEIR model as depicted by
Figure I.

techniques. In the numerical method, stability and convergence should be

which introduce an embedding parameter to construct a homotopy and then
analyzes it by means of Taylor formula. Therefore, unlike the perturbation

190

Jaharuddin

Homotopy Perturbation Method for a SEIR Model ...
subject to the initial conditions

;t {

€E

191

S(O) セ@

0, E(O) セ@ 0, 1(0) セ@ 0, /1(0) セ@

0.

The total population size N(t) can be determined by N(t) = S(t) + E(t)

Figure I. A schematic representation of the flow of individuals between

+ l(t) + R(t) or from the differential equation

epidemiological classes.

dN = (b _ d)N - a.I,
dt

The parameter h > 0 is the constant rate for natural birth and d > 0 is
that of natural death. It is assumed that all newborns arc susceptible and

(2)

which is derived by adding the equations in ( l ).

vertical transmission can be neglected. l'hc parameter a is the constant rate
3. Analysis of Method

for disease-related death and y is the rate for recovery. The rate of removal e
of individuals from the exposed class is assumed lo be a constant so that

l/t

can be regarded as the mean latent period. In the limiting case, when
E

-> oo, or equivalently, when the mean latent period lfe -> 0, the SEIR

In this section, we illustrate the basic idea of the homotopy perturbation
method for solving nonlinear differential equation in which we consider the
following general nonlinear problem:

model becomes a SIR model. The recovered individuals are assumed to

A(u(r)) = 0, r

ac.quire permanent immunity; there is no transfer from R class back to the S

E Q,

(3)

class. The per capita contact rate A., which is the average number of effective

where A is a nonlinear operator, u(r) is an unknown function, r is an

co_ntacts with other individual hosts per unit time, is then a constant. A

independent variable, and

fraction l(t)/ N(t) of these contacts is with infectious individuals and thus

v(r, p) : n x [O, l] -> IR which satisfies

the average number of relevant contacts of each individual with the

n

is the domain. W c construct a homotopy

H(v, p) = (1 - p)(L(v)- L(v0 )) + pA(v),

'infectious class is A.i(t)/ N(r). The total number of new infections at a time t

l]

is an embedding parameter, L denotes an auxiliary linear

is given by A.l(t)S(t)/ N(t). The following differential equations are derived

where p e [0,

based on the basic assumption and using the transfer diagram:

operator and v0 is an initial approximation of the exact solution. By equating

dS
dt

to zero the homotopy function, the zero-order deformation equation is
=

bN - dS _ A.IS

constructed as

N'

(1 - p)(L(v)- L(vo)) + pA(v) = 0.

(4)

dE _ A.IS _ (t + d)E,

dt -

N

Setting p = 0, the zero-order deformation equation (4) becomes

di
dt = EE - (y +CJ.+ d)I,

L(v)-L(vo) = 0.
Using (5), by linearity

dR
dt

= yl -

dR,

(I)

v(r, 0) = vo(r).

(5)

,,,,

Jahamddin

Homotopy Perturbation Method for a SEIR Model ...

When p = 1, the zero-order deformation equation (4) is reduced to

dr
d1 = yi - br + air,

193

(8)

A(v(r, I))= 0,
subject to the restriction s + e + i + r = I. Note that the total population size

which is exactly the same as the nonlinear equation (3 ), provided

N(I) does not appear in (8); this is a direct of the homogeneity of the system

v(r, I)= 11(r).

(8). Also observe that the variable r does not appear in the first three
According to the homotopy perturbation method, the solution of the
equation (4) can be expressed as a series inp in the form:

= VQ

V

+

fJVI

+p

2

V2

+ · · ·.

equations of (8). This allows us to attack (8) by studying the subsystem:
ds =b-bs-f.is+ais,
di

(6)

When p-> I, equation (4) corresponds to the original equations (3) and (6)

セ[@

becomes the approximate solution of equation (3), i.e.,
ll

lim v =

=

Vo

+

V1

+ V2 + ....

(7)

= f.is - (E + h )e + aie,

di
.2
di =Ee- (y+a.+ I)'
Jl+fJ.I,

ーセi@

The convergence of the series in equation (7) is discussed by He in [5].

(9)

and determining r from r = I - s - e - r or

4. Application of Method

dr
di = yi - hr + a.ir.

In this section, the homotopy perturbation method described in the
previous section for solving a SEIR model with varying total population size

Subsystem (9) will be solved by generalizing the described homotopy

is applied. Then comparison is made with the numerical method to assess the
accuracy and the effectiveness of the homotopy perturbation method. The

perturbation method. The linear operators L1, l2, and L3 can be defined as
below:

first step is to transform the variables.
Let s = S/N, e

= E/N, i = I/N,

and r

= R/N

.) d• '-() de'-(')
di
l(
I S = di ' セl@
e = di ' セj@ 1 = di .

denote the fractions of

the classes S, E. I. and R in the population, respectively. It is easy to verify
thats, e, i, and r satisfy the system of differential equations:

From (9) nonlinear operators A1, A2 , and A3 can be defined as

d1· = h _ hs _;\.is + a.is,

A1(s) =

de
, . - (E + b) e + a1e,
.
dt = A.ls

Ai(e) =

d1

di
( y+a.+ b)'l+fJ.I,
.2
-,=Eeal

l

A3(i)

]セ[Me・K@

セ@
セ[@

- b + hs + f.is - ais,

- f.is + (E + b)e - a.ie,

(y +a+ b)i - ai2.

• 194

Homotopy Perturbation Method for a SEIR Model ...

Jaharuddin

ei = [ai0 eo + 'J...i0 s0

According to equation (4 ). we can obtain

dt

di

Coefficient of

de -deo)
(1-p) ( - +p(de
--'J...is+(r.+h)e-aie ) =0
dtdl

HQMーIセ@

dt

MZセI@

'

+ 1{:;-r.e+(y+a +h)i-ai2) = 0,

(10)

so(t) = s(O), e0(1) = e(O), i0(t) = i(O).

,\' = SQ + fJSJ + fl 2Sz + p .1 S3 + "·,

s2 =

Mセィ{「@

2.

";7

= -bs1 - ('J... - a) (ios1 + i1so ),

d;7

= 'J...(i1s 0 + i0s1) + a(i0 e1 + i1eo)-(r. + b)ei,

- bs0

e -- eo + pe1 + p 2ez + p 3e3 + ... ,
.

gives the following initial value problem:

with initial conditions: s 2(0) = 0, e2(0) = 0, i2(0) = 0. Solving the above
equations, we obtain the following approximations:

In the following we assume the solution for system (I 0) in the form:

.

p2

diz
(
/)'1 + 2··
dt=r.e1+y+a+>1
at0 11,

and the initial approximations arc as follows:

.

+ b)eo]t,

it = [r.eo -(y +a+ b)i0 + ai5]t.

(I_ p)(ds - di·o) + p(d' - h + hs +/...is - ais) = 0,

di

- (r.

195

J.

1 = 10 + P11 + P 12 + P 13 + .. "

- ('J... - a)i0s 0 ]1

P H「@
。I{セゥ

-('J... (I I)

+

セ{イN・ッ@

- bs 0

2

- ('J... -

a)i0 s0 )1

2

-(y +a+ b)io + ai6Js 0 t

J.

2

Substituting equation ( 11) into (I 0) and equating the term with identical
powers of p, we obtain the set of initial value problems. Coefficient of p

e2 =

セGjN{イ・

P@

gives the following initial value problem:

+

.

, .

(

= atoeo + "''o"o - r. +

h) eo,
-

dii = i:e0 - (y +a+ h)io + ai6,

d1

with initial conditions: s 1(0) = 0, e1(0) = 0, i1(0) = 0. Solving the above
equations, we obtain the following approximations:

s 1 = [h - hs0

- ('J... -

a)i0so]t,

2
(y +a+ b)i0 + ai5Js0 t +

+ -'-ai0 [ai0e0 + 'J...i0 s0 - (r. + b)e0 ]t
2

d'1 = ;, _ h.i·o - ('J... - a)ioso.
di
de1
dr

-

i2 =

セ。{イN・

P@

-

- (r. +

-'-r.[ai0 e0 + 'J...i0 s0 -(r. + b)e0 ]t

P {「@

- bs0 - ('J... - a)i0so]t

2

(y +a+ b)i0 + ai5Je0 t

セ@ (r. + b)[ai0e0 + 'J...i0 s0

セGjNゥ

2

2
b)e0 ]t ,

2

2

+ セHケ@

+a+ b)[r.eo - (y +a+ b)i0 + ai5]t

2

+ aio[r.eo -(y +a+ b)io + ai5Jt ,

2

2

• 196

Jaharuddin

Homotopy Perturbation Method for a SEIR Model ...

and so on, in the same manner the rest of the components can be obtained

Table 2. Comparison between absolute error of homotopy perturbation
ethod (HPM) and numerical method (NM)

using the symbolic package. According to the homotopy perturbation
method, we can obtain the solution in a series formed as follows:

I
S ::::

so

+ SI + .'lz + ,.. '

197

Is(t)HPM -s(t)NM I Ie(t)HPM -e(t)NM I Ii(t)HPM -i(l)NM I

0

0

0

0

0.1

3.0000 x 10-IO

3.6000 x 10- 10

2.2769 x 10-1

{12)

0.2

2. 7000 x 10-9

2.7600 x 10-9

9.1061x10-1

Suppose given the following data: the initial number of susceptible

0.3

8.9000 x 10-9

9.3200 x 10-9

2.0485 x 10-6

0.4

2.1200 x 10-8

2.2050 x 10-8

3.6413 x 10-6

0.5

4.1500 x 10-8

4.30 I 0 x 10-8

5.6887 x 10-6

0.6

7.1600 x 10-8

7.4700 x 10-8

8.1902x10-6

0.7

1.1400 x 10-1

l.1922x 10-7

1.1146 x 10-5

0.8

1.7040 x 10-1

1.7842 x 10-1

1.4554 x 10-5

0.9

2.4260 x 10-1

2.5412 x J0- 7

1.8418 x 10-5

1

3.3290 x 10-1

3.4813 x 10-1

2.2734 x 10-5

e = e0 + e1 + ez + ···,
i=io+ii+iz+···.

individual in the location S(O) = JO thousand: the initial number of expose
people 1:"(0) = I thousand: initial number of actively infected people
/(0) = O: The parameter values used for numerical simulation is given in
Table I.
Table I. Values used in the numerical simulation [2]

A.

The parameter controlling how ollen a susceptibleinfected contact results in a new exposure

y

The rate an infected recovers and moves into the

resistant phase

"

The rate at which an exposed person becomes
infective

b

The natural birth rate

a

The rate for diseases related death

0.05

0.003

0.05

5. Conclusions
In this paper, homotopy perturbation method has been successfully

0.00001

applied to find the solution of the SEIR model with varying total population
0.002

size. The method is reliable and easy to use. The main advantage of the

Then following approximate solution is obtained as result of first 6

method is the fact that it provides its user with an analytical approximation,

terms of the series decomposition {12). Results calculated by homotopy

in many cases an exact solution, in a rapidly convergent sequence with

perturbation method arc compared with numerical solution in Table 2. The

elegantly computed term.

explicit Rungc-Kutta method in symbolic computation package has been
References

used to find numerical solution of s(t), e(l), and i(t). As it can be seen in
Table 2, there exists a very good agreement between homotopy perturbation
method result and numerical solutions.

[I]

J. E. Cohen, Infectious diseases of hu1nans: dynamics and control, The Journal of
the American Medical Association 268 (1992), 3381-3392.

198

Jaharuddin

[21

E. Dcmirci, A. Unal and N. Ozalp, A fractional order SEIR model with density
dependent dca!h rate, Hacct J. Ma!h. Slat 40 (2011), 287-295.

{3)

A. Fercidoon, H. Yaghoobi and M. Davoudabadi, Application of the homotopy
perturbation method for solving the foam drainage equation, Int. J. Differ. Equ.
2011, Art. ID 864023, 13 pp. doi:I0.1155/2011/864023.

[4]

J. 1-1. lie, A coupling method of a homotopy technique and a perturbation
technique ICJr non-linear problerns, Internal. J. Non-Linear Mech. 35 (2000),
37-43.

[5]

J. II. He, Homotopy perturbation method: a ne\v nonlinear analytical technique,
Appl. Ma!h. Compu!. 135 (2003), 73-79.

!61

J. 1-1. He. Ho1notopy perturbation technique, Comput. Methods Appl. Mech.
Engrg. 178(3-4) ( 1999), 257-262.

(7]

X. Li and B. Fang, Stability of an age-structured SEIR epidemic model with
infcc1ivi1y in la!en! period, Appl. Appl. Math. 4 (2009), 218-236.

(81

M. Y. Li and J. S. Muldowney, A geometric approach to global-stability
problems. SIAM J. Math. Anal. 27 (1996), 1070-1083.

[91

S. J. Liao, The proposed homotopy analysis technique for rhc solutions of
nonlinear problems, Ph.D. dissertation, Shanghai Jiao Tong University, China,
1992.

[10]

M. Y. Li, J. R. Graef, L. C. Wang and J. Karsai, Global dynamics of a SEIR
model with varying total population size, Math. Biosci. 160 ( 1999), 191-213.

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...

,. '·
セ@

ᄋMGBZセO@



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セイZェMNA@

.

,,_,/·'·A· ..

• ii;idla

•.;:-:::t

I'

/;:•'

·,:;_,.:A.
/.

;-,.:
·t--

. (.--

.,

ᄋHセLN[@



--

'J

セM[ᄋ⦅@

/.

Mセイᄋ

イMᄋセQ@

.' '•
j ....

,. .!':J·:.

セ@

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/.

..rr- ·.·.· :·,,,,.../
i'·

J

·--;'-/

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;•.-.{-

.·;·

!itf
c
,

--,I'.

ᄋセ@

·t.

;-< .•..Gセ@ :-.,- ·. ·

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