 Review Article
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A Survey on Oscillation of Impulsive Ordinary Differential Equations
Advances in Difference Equations volume 2010, Article number: 354841 (2010)
Abstract
This paper summarizes a series of results on the oscillation of impulsive ordinary differential equations. We consider linear, halflinear, superhalflinear, and nonlinear equations. Several oscillation criteria are given. The Sturmian comparison theory for linear and half linear equations is also included.
1. Introduction
Impulsive differential equations, that is, differential equations involving impulse effect, appear as a natural description of observed evolution phenomena of several real world problems. There are many good monographs on the impulsive differential equations [1–6]. It is known that many biological phenomena, involving thresholds, bursting rhythm models in medicine and biology, optimal control models in economics, pharmacokinetics, and frequency modulates systems, do exhibit impulse effects. Let us describe the KrugerThiemer model [7] for drug distribution to show how impulses occur naturally. It is assumed that the drug, which is administered orally, is first dissolved into the gastrointestinal tract. The drug is then absorbed into the socalled apparent volume of distribution and finally eliminated from the system by the kidneys. Let and denote the amounts of drug at time in the gastrointestinal tract and apparent volume of distribution, respectively, and let and be the relevant rate constants. For simplicity, assume that The dynamic description of this model is then given by
In [8], the authors postulate the following control problem. At discrete instants of time , the drug is ingested in amounts This imposes the following boundary conditions:
To achieve the desired therapeutic effect, it is required that the amount of drug in the apparent volume of distribution never goes below a constant level or plateau say, during the time interval where . Thus, we have the constraint
It is also assumed that only nonnegative amounts of the drug can be given. Then, a control vector is a point in the nonnegative orthant of Euclidean space of dimension . Hence, . Finally, the biological cost function minimizes both the side effects and the cost of the drug. The problem is to find subject to (1.1)–(1.3).
The first investigation on the oscillation theory of impulsive differential equations was published in 1989 [9]. In that paper Gopalsamy and Zhang consider impulsive delay differential equations of the form
where as and is a positive real number. Sufficient conditions are obtained for the asymptotic stability of the zero solution of (1.4) and existence of oscillatory solutions of (1.5). However, it seems that the problem of oscillation of ordinary differential equations with impulses has received attention much later [10]. Although, the theory of impulsive differential equations has been well established, the oscillation theory of such equations has developed rather slowly. To the best of our knowledge, except one paper [11], all of the investigations have been on differential equations subject to fixed moments of impulse effect. In [11], secondorder differential equations with random impulses were dealt with, and there are no papers on the oscillation of differential equations with impulses at variable times.
In this survey paper, our aim is to present the results (within our reach) obtained so far on the oscillation theory of impulsive ordinary differential equations. The paper is organized as follows. Section 2 includes notations, definitions, and some wellknown oscillation theorems needed in later sections. In Section 3, we are concerned with linear impulsive differential equations. In Section 4, we deal with nonlinear impulsive differential equations.
2. Preliminaries
In this section, we introduce notations, definitions, and some wellknown results which will be used in this survey paper.
Let for some fixed and be a sequence in such that and
By we denote the set of all functions which are continuous for and continuous from the left with discontinuities of the first kind at Similarly, is the set of functions having derivative . One has , , or . In case , we simply write for . As usual, denotes the set of continuous functions from to .
Consider the system of firstorder impulsive ordinary differential equations having impulses at fixed moments of the form
where , , and
with . The notation in place of is also used. For simplicity, it is usually assumed that .
The qualitative theory of impulsive ordinary differential equations of the form (2.1) can be found in [1–6, 12].
Definition 2.1.
A function is said to be a solution of (2.1) in an interval if satisfies (2.1) for .
For , we may impose the initial condition
Each solution of (2.1) which is defined in the interval and satisfying the condition is said to be a solution of the initial value problem (2.1)(2.3).
Note that if then the solution of the initial value problem (2.1)(2.3) coincides with the solution of
on .
Definition 2.2.
A realvalued function , not necessarily a solution, is said to be oscillatory, if it is neither eventually positive nor eventually negative. Otherwise, it is called nonoscillatory. A differential equation is called oscillatory if all its solutions are oscillatory.
For our purpose we now state some wellknown results on oscillation of secondorder ordinary differential equations without impulses.
Theorem 2.3 (see [13]).
Let Then, the equation
is oscillatory if
and nonoscillatory if
Theorem 2.4 (see [14]).
Let and be continuous functions and . If
then the equation
is oscillatory.
Theorem 2.5 (see [15]).
Let be a positive and continuously differentiable function for and let If
then the equation
has nonoscillatory solutions, where is an integer.
Theorem 2.6 (see [15]).
Let be a positive and continuous function for and an integer. Then every solution of (2.11) is oscillatory if and only if
3. Linear Equations
In this section, we consider the oscillation problem for first, second, and higherorder linear impulsive differential equations. Moreover, the Sturm type comparison theorems for secondorder linear impulsive differential equations are included.
3.1. Oscillation of FirstOrder Linear Equations
Let us consider the linear impulsive differential equation
together with the corresponding inequalities:
The following theorems are proved in [1].
Theorem 3.1.
Let and Then the following assertions are equivalent.

(1)
The sequence has infinitely many negative terms.

(2)
The inequality (3.2) has no eventually positive solution.

(3)
The inequality (3.3) has no eventually negative solution.

(4)
Each nonzero solution of (3.1) is oscillatory.
Proof.
(1)(2) Let the sequence have infinitely many negative terms. Let us suppose that the assertion () is not true; that is, the inequality (3.2) has an eventually positive solution Let be such that Then, it follows from (3.2) that
which is a contradiction.
(2)(3). The validity of this relation follows from the fact that if is a solution of the inequality (3.2), then is a solution of the inequality (3.3) and vice versa.
(2) and (3) (4) In fact, if (3.1) has neither an eventually positive nor an eventually negative solution, then each nonzero solution of (3.1) is oscillatory.
(4)(1) If is an oscillatory solution of (3.3), then it follows from the equality
that the sequence has infinitely many negative terms.
The following theorem can be proved similarly.
Theorem 3.2.
Let and Then the following assertions are equivalent.

(1)
The sequence has finitely many negative terms.

(2)
The inequality (3.2) has an eventually positive solution.

(3)
The inequality (3.3) has an eventually negative solution.

(4)
Each nonzero solution of (3.1) is nonoscillatory.
It is known that (3.1) without impulses has no oscillatory solutions. But (3.1) (with impulses) can have oscillatory solutions. So, impulse actions determine the oscillatory properties of firstorder linear differential equations.
3.2. Sturmian Theory for SecondOrder Linear Equations
It is wellknown that Sturm comparison theory plays an important role in the study of qualitative properties of the solutions of both linear and nonlinear equations. The first paper on the Sturm theory of impulsive differential equations was published in 1996. In [10], Bainov et al. derived a Sturmian type comparison theorem, a zerosseparation theorem, and a dichotomy theorem for secondorder linear impulsive differential equations. Recently, the theory has been extended in various directions in [16–18], with emphasis on Picone's formulas, Wirtinger type inequalities, and Leighton type comparison theorems.
We begin with a series of results contained in [1, 10]. The secondorder linear impulsive differential equations considered are
where and are continuous for and they have a discontinuity of the first kind at the points where they are continuous from the left.
The main result is the following theorem, which is also valid for differential inequalities.
Suppose the following.

(1)
Equation (3.7) has a solution such that
(3.8)

(2)
The following inequalities are valid:
(3.9)

(3)
in a subinterval of or for some
Then (3.6) has no positive solution defined on
Proof.
Assume that (3.6) has a solution such that Then from the relation
an integration yields
From (3.6), (3.7), condition (), and the above inequality, we conclude that
But, from conditions () and (), it follows that the right side of the above inequality is negative, which leads to a contradiction. This completes the proof.
The following corollaries follow easily from Theorem 3.3.
Corollary 3.4 (Comparison Theorem).
Suppose the following.

(1)
Equation (3.7) has a solution such that
(3.13)

(2)
The following inequalities are valid:
(3.14)

(3)
in some subinterval of or for some
Then, each solution of (3.6) has at least one zero in
Corollary 3.5.
If conditions ( 1) and ( 2) of Corollary 3.4 are satisfied, then one has the following.

(1)
Each solution of (3.6) for which has at least one zero in

(2)
Each solution of (3.6) has at least one zero in
Corollary 3.6 (Oscillation Theorem).
Suppose the following.

(1)
There exists a solution of (3.7) and a sequence of disjoint intervals such that
(3.15)
for

(2)
The following inequalities are valid for and ;
(3.16)
Then all solutions of (3.6) are oscillatory, and moreover, they change sign in each interval
Corollary 3.7 (Comparison Theorem).
Let the inequalities hold for and Then, all solutions of (3.7) are nonoscillatory if (3.6) has a nonoscillatory solution.
Corollary 3.8 (Separation Theorem).
The zeros of two linearly independent solutions of (3.6) separate one another; that is, the two solutions have no common zeros, and if are two consecutive zeros of one of the solutions, then the interval contains exactly one zero of the other solution.
Corollary 3.9 (Dichotomy Theorem).
All solutions of (3.6) are oscillatory or nonoscillatory.
We can use Corollary 3.7, to deduce the following oscillation result for the equation:
Suppose the following.

(1)
The function is such that if is a continuous function for having a piecewise continuous derivative for then the function is piecewise continuous for

(2)
The following inequalities are valid:
(3.18)
Then every solution of (3.17) defined for is oscillatory if (3.7) has an oscillatory solution.
Recently, by establishing a Picone's formula and a Wirtinger type inequality, Özbekler and Zafer [17] have obtained similar results for secondorder linear impulsive differential equations of the form
where and are real sequences, with and for all
Let be a nondegenerate subinterval of . In what follows we shall make use of the following condition:
It is wellknown that condition (H) is crucial in obtaining a Picone's formula in the case when impulses are absent. If (H) fails to hold, then Wirtinger, Leighton, and SturmPicone type results require employing a socalled "device of Picard." We will show how this is possible for impulsive differential equations as well.
Let (H) be satisfied. Suppose that such that and . These conditions simply mean that and are in the domain of and , respectively. If for any , then we may define
For clarity, we suppress the variable . Clearly,
In view of (3.19) and (3.20) it is not difficult to see from (3.22) that
Employing the identity
the following Picone's formula is easily obtained.
Theorem 3.11 (Picone's formula [17]).
Let (H) be satisfied. Suppose that such that and . If for any and then
In a similar manner one may derive a Wirtinger type inequality.
Theorem 3.12 (Wirtinger type inequality [17]).
If there exists a solution of (3.19) such that on , then
where
Corollary 3.13.
If there exists an such that then every solution of (3.19) has a zero in .
Corollary 3.14.
Suppose that for a given there exists an interval and a function for which . Then (3.19) is oscillatory.
Next, we give a Leighton type comparison theorem.
Theorem 3.15 (Leighton type comparison [17]).
Suppose that there exists a solution of (3.19). If (H) is satisfied with and
then every solution of (3.20) must have at least one zero in .
Proof.
Let and . Since and are solutions of (3.19) and (3.20), respectively, we have . Employing Picone's formula (3.25), we see that
The functions under integral sign are all integrable, and regardless of the values of or , the lefthand side of (3.29) tends to zero as . Clearly, (3.29) results in
which contradicts (3.28).
Corollary 3.16 (SturmPicone type comparison).
Let be a solution of (3.19) having two consecutive zeros . Suppose that (H) holds, and
for all , and
for all for which .
If either (3.31) or (3.32) is strict in a subinterval of or (3.33) is strict for some , then every solution of (3.20) must have at least one zero on .
Corollary 3.17.
Suppose that conditions (3.31)(3.32) are satisfied for all for some integer , and that (3.33) is satisfied for all for which . If one of the inequalities (3.31)–(3.33) is strict, then (3.20) is oscillatory whenever any solution of (3.19) is oscillatory.
As a consequence of Theorem 3.15 and Corollary 3.16, we have the following oscillation result.
Corollary 3.18.
Suppose for a given there exists an interval for which that condition of either Theorem 3.15 or Corollary 3.16 are satisfied. Then (3.20) is oscillatory.
If (H) does not hold, we introduce a setting, which is based on a device of Picard, leading to different versions of Corollary 3.16.
Indeed, for any we have
Let
It follows that
Assuming that , the choice of yields
Then, we have the following result.
Theorem 3.19 (Device of Picard [17]).
Let and let be a solution of (3.19) having two consecutive zeros and in . Suppose that
are satisfied for all , and that
for all for which .
If either (3.38) or (3.39) is strict in a subinterval of or (3.40) is strict for some , then any solution of (3.20) must have at least one zero in .
Corollary 3.20.
Suppose that (3.38)(3.39) are satisfied for all for some integer , and that (3.40) is satisfied for all for which . If and one of the inequalities (3.38)–(3.40) is strict, then (3.20) is oscillatory whenever any solution of (3.19) is oscillatory.
As a consequence of Theorem 3.19, we have the following Leighton type comparison result which is analogous to Theorem 3.15.
Theorem 3.21 (Leighton type comparison [17]).
Let . If there exists a solution of (3.19) such that
then every solution of (3.20) must have at least one zero in .
As a consequence of Theorems 3.19 and 3.21, we have the following oscillation result.
Corollary 3.22.
Suppose that for a given there exists an interval for which conditions of either Theorem 3.19 or Theorem 3.21 are satisfied. Then (3.20) is oscillatory.
Moreover, it is possible to obtain results for (3.20) analogous to Theorem 3.12 and Corollary 3.13.
Theorem 3.23 (Wirtinger type inequality [17]).
If there exists a solution of (3.20) such that on , then for and for all
Corollary 3.24.
If there exists an with such that then every solution of (3.20) must have at least one zero in .
As an immediate consequence of Corollary 3.24, we have the following oscillation result.
Corollary 3.25.
Suppose that for a given there exists an interval and a function with for which . Then (3.20) is oscillatory.
3.3. Oscillation of SecondOrder Linear Equations
The oscillation theory of secondorder impulsive differential equations has developed rapidly in the last decade. For linear equations, we refer to the papers [11, 19–21].
Let us consider the secondorder linear differential equation with impulses
where , and are two known sequences of real numbers, and
For (3.43), it is clear that if for all large then (3.43) is oscillatory. So, we assume that The following theorem gives the relation between the existence of oscillatory solutions of (3.43) and the existence of oscillatory solutions of secondorder linear nonimpulsive differential equation:
Theorem 3.26 (see [19]).
Assume that Then the oscillation of all solutions of (3.43) is equivalent to the oscillation of all solutions of (3.45).
Proof.
Let be any solution of (3.43). Set for Then, for all we have
Thus, is continuous on Furthermore, for we have
For it can be shown that
Thus, is continuous if we define the value of at as
Now, we have for
and for
Thus, we obtain
This shows that is the solution of (3.45).
Conversely, if is the continuous solution of (3.45), we set for Then, and Furthermore, for we have
and so
Thus, is the solution of (3.43). This completes the proof.
By Theorems 3.26 and 2.3, one may easily get the following corollary.
Corollary 3.27.
Assume that . Then, (3.43) is oscillatory if
and nonoscillatory if
When and oscillation criteria for (3.43) can be obtained by means of a Riccati technique as well. First, we need the following lemma.
Lemma 3.28.
Assume that on any interval and let be an eventually positive solution of (3.43). If
where then, eventually
Now, let be an eventually positive solution of (3.43) such that and for Under conditions of Lemma 3.28, let for Then, (3.43) leads to an impulsive Riccati equation:
where
Theorem 3.29 (see [19]).
Equation (3.43) is oscillatory if the secondorder selfadjoint differential equation
is oscillatory, where
Proof.
Assume, for the sake of contradiction, that (3.43) has a nonoscillatory solution such that for Now, define
Then, it can be shown that is continuous and satisfies
Next, we define
Then is a solution of (3.59). This completes the proof.
By Theorems 3.29 and 2.4, we have the following corollary.
Corollary 3.30.
Assume that
where Then, (3.43) is oscillatory.
Example 3.31 (see [19]).
Consider the equation
If for some integer then it is easy to see that
where denotes the greatest integer function, and
Thus, by Corollary 3.30, (3.64) is oscillatory. We note that the corresponding differential equation without impulses
is nonoscillatory by Theorem 2.3.
In [20], Luo and Shen used the above method to discuss the oscillation and nonoscillation of the secondorder differential equation:
where
In [21], the oscillatory and nonoscillatory properties of the secondorder linear impulsive differential equation
is investigated, where
for all and is the function, that is,
for all being continuous at Before giving the main result, we need the following lemmas. For each define the sequence inductively by
where provided and provided Let
Lemma 3.32.
If for some then and for all
Proof.
By induction and in view of the fact that the function is increasing in it can be seen that
Hence,
The next lemma can also be proved by induction.
Lemma 3.33.
Suppose that and for all Define, by induction,
If for all then
The following theorem is the main result of [21]. The proof uses the above two lemmas and the induction principle.
Theorem 3.34.
The following statements are equivalent.

(i)
There is such that

(ii)
There is such that for all

(iii)
Equation (3.69) is nonoscillatory.

(iv)
Equation (3.69) has a nonoscillatory solution.
Applying Theorem 3.34, the nonoscillation and oscillation of (3.69), in the case of and are investigated in [21].
In all the publications mentioned above, the authors have considered differential equations with fixed moments of impulse actions. That is, it is assumed that the jumps happen at fixed points. However, jumps can be at random points as well. The oscillation of impulsive differential equations with random impulses was investigated in [11]. Below we give the results obtained in this case.
Let be a random variable defined in and let be a constant. Consider the secondorder linear differential equation with random impulses:
where are Lebesque measurable and locally essentially bounded functions, , for all and
Definition 3.35.
Let be a realvalued random variable in the probability space where is the sample space, is the field, and is the probability measure. If , then is called the expectation of and is denoted by that is,
In particular, if is a continuous random variable having probability density function then
Definition 3.36.
A stochastic process is said to be a sample path solution to(3.76) with the initial condition if for any sample value of then satisfies
Definition 3.37.
The exponential distribution is a continuous random variable with the probability density function:
where is a parameter.
Definition 3.38.
A solution of (3.76) is said to be nonoscillatory in mean if is either eventually positive or eventually negative. Otherwise, it is called oscillatory.
Consider the following auxiliary differential equation:
Lemma 3.39.
The function is a solution of (3.76) if and only if
where is a solution of (3.81) with the same initial conditions for (3.76), and is the index function, that is,
Proof.
If is a solution of system (3.81), for any we have
It can be seen that
which imply that satisfies (3.76), that is, is a sample path solution of (3.76). If is a sample path solution of (3.76), then it is easy to check that is a solution of (3.81). This completes the proof.
Theorem 3.40 (see [11]).
Let the following condition hold.
(C) Let be exponential distribution with parameter , and let be independent of if
If there exists such that
does not change sign for all then all solutions of (3.76) are oscillatory in mean if and only if all solutions of (3.81) are oscillatory.
Proof.
Let be any sample path solution of (3.76); then Lemma 3.39 implies
where is a solution of (3.81). Hence,
Further, it can be seen that
So,
By assumption, has the same sign as for all That is, all solutions of (3.76) are oscillatory in mean if and only if all solutions of (3.81) are oscillatory. This completes the proof.
When is finite, , then the following result can be proved.
Theorem 3.41 (see [11]).
Let condition (C) hold, and let be finite for all . Further assume that there are a finite number of such that Then all solutions of (3.76) are oscillatory in mean if and only if all solutions of (3.81) are oscillatory.
3.4. Oscillation of HigherOrder Linear Equations
Unlike the secondorder impulsive differential equations, there are only very few papers on the oscillation of higherorder linear impulsive differential equations. Below we provide some results for thirdorder equations given in [22]. For higherorder liner impulsive differential equations we refer to the papers [23, 24].
Let us consider the thirdorder linear impulsive differential equation of the form
where and is not always zero in for sufficiently large
The following lemma is a generalization of Lemma in [25].
Lemma 3.42 (see [22]).
Assume that is a solution of (3.91) and there exists such that for any Let the following conditions be fulfilled.
One has
One has
Then for sufficiently large either or holds, where
(A) one has
(B) one has
Theorem 3.43 (see [22]).
Assume that conditions of Lemma 3.42 are fulfilled and for any and Moreover, assume that the sequence of numbers has a positive lower bound, converges, and holds. Then every bounded solution of (3.91) either oscillates or tends asymptotically to zero with fixed sign.
Proof.
Suppose that is a bounded nonoscillatory solution of (3.91) and According to Lemma 3.42, either or is satisfied. We claim that does not hold. Otherwise, for some Since it follows that is monotonically increasing for For any , By induction, it can be seen that
in particular,
Integrating from to we obtain
By induction, for any natural number we have
Considering the condition in Lemma 3.42 and the sequence of numbers has a positive lower bound, we conclude that the inequality above leads to a contradiction that the right side tends to while is bounded. Therefore, case holds. implies that is strictly monotonically decreasing. From the facts that the series converges and is bounded, it follows that converges and there exists limit where Now, we claim that Otherwise, and there exists such that for From (3.91) and the last inequality, we can deduce
Integrating by parts of the above inequality and considering and , we have the following inequality:
Since and the series converges, the above inequality contradicts the fact that is bounded, hence , and the proof is complete.
The proof of the following theorem is similar.
Theorem 3.44 (see [22]).
Assume that conditions of Lemma 3.42 hold and for any , and Moreover, assume that the sequence of numbers is bounded above, converges, and holds. Then every solution of (3.91) either oscillates or tends asymptotically to zero with fixed sign.
Some results similar to the above theorems have been obtained for fourthorder linear impulsive differential equations; see [24].
4. Nonlinear Equations
In this section we present several oscillation theorems known for superliner, halflinear, superhalflinear, and fully nonlinear impulsive differential equations of second and higherorders. We begin with Sturmian and Leighton type comparison theorems for halflinear equations.
4.1. Sturmian Theory for HalfLinear Equations
Consider the secondorder half linear impulsive differential equations of the form:
where and are real sequences, and with and
The lemma below can be found in [26].
Lemma 4.1.
Let and be a constant; then
where equality holds if and only if .
The results of this section are from [16].
Theorem 4.2 (SturmPicone type comparison).
Let be a solution of (4.1) having two consecutive zeros and in . Suppose that and are satisfied for all , and that for all for which . If either or or , then any solution of (4.2) must have at least one zero in .
Proof.
Assume that never vanishes on . Define
where the dependence on of the solutions and is suppressed. It is not difficult to see that
Clearly, the last term of (4.5) is integrable over if and . Moreover, in this case. Suppose that . The case is similar. Since and
we get
and so
Moreover,
Integrating (4.5) from to and using (4.6), we see that
where we have used Lemma 4.1 with , , and . It is clear that (4.11) is not possible under our assumptions, and hence must have a zero in .
Corollary 4.3 (Separation Theorem).
The zeros of two linearly independent solutions and of (4.1) separate each other.
Corollary 4.4 (Comparison Theorem).
Suppose that and are satisfied for all for some , and that for all for which . If either or or , then every solution of (4.2) is oscillatory whenever a solution of (4.1) is oscillatory.
Corollary 4.5 (Dichotomy Theorem).
The solutions of (4.1) are either all oscillatory or all nonoscillatory.
Theorem 4.6 (Leightontype Comparison).
Let be a solution of (4.1) having two consecutive zeros and in . Suppose that
Then any nontrivial solution of (4.2) must have at least one zero in .
Proof.
Assume that has no zero in . Define the function as in (4.4).
Clearly, (4.5) and (4.6) hold. It follows that
which is a contradiction. Therefore, must have a zero on .
If , then we may conclude that either has a zero in or is a constant multiple of .
As a consequence of Theorems 4.2 and 4.6, we have the following oscillation result.
Corollary 4.7.
Suppose for a given there exists an interval for which either conditions of Theorem 4.2 or Theorem 4.6 are satisfied, then every solution of (4.2) is oscillatory.
4.2. Oscillation of SecondOrder Superlinear and SuperHalfLinear Equations
Let us consider the forced superlinear secondorder differential equation of the following form:
where denotes the impulse moments sequence with
Assume that the following conditions hold.
() is a constant, is a continuous function, .
() are constants,
() and are two intervals such that with for and for for
Interval oscillation criteria for (4.14) are given in [27]. Denote and for let
Theorem 4.8 (see [27]).
Assume that conditions (A1)–(A3) hold, and that there exists such that
where for and
for Then every solution of (4.14) has at least one zero in
Proof.
Let be a solution of (4.14). Suppose that does not have any zero in Without loss of generality, we may assume that for Define
Then, by Hölder's inequality, for and we have
For we obtain
If then all impulsive moments are in Multiplying both sides of (4.19) by and integrating on and using the hypotheses, we get
On the other hand, for it follows that
which implies that is nonincreasing on So, for any one has
It follows from the above inequality that
Making a similar analysis on we obtain
From (4.21)–(4.25) and we get
which contradicts (4.16). If then and there are no impulse moments in Similarly to the proof of (4.21), we get
which again contradicts (4.16).
In the case one can repeat the above procedure on the subinterval in place of This completes the proof.
Corollary 4.9.
Assume that conditions (A1) and (A2) hold. If for any there exist satisfying (A3) with and satisfying (4.16), then (4.14) is oscillatory.
The proof of following theorem is similar to that of Theorem 4.8.
Theorem 4.10 (see [27]).
Assume that conditions (A1)–(A3) hold, and there exists a such that
where for and
for Then every solution of (4.14) has at least one zero in
Corollary 4.11.
Assume that conditions (A1) and (A2) hold. If for any there exist satisfying (A3) with and satisfying (4.28), then (4.14) is oscillatory.
Example 4.12.
Consider the following superlinear impulsive differential equation:
It can be seen that if
then, conditions of Corollary 4.9 are satisfied; here is the gamma function, and and satisfy (2). So, every solution of (4.30) is oscillatory.
In [28–30], the authors have used an energy function approach to obtain conditions for the existence of oscillatory or nonoscillatory solutions of the halflinear impulsive differential equations of the following form:
where for
Define the energy functional
where in explicit form and The functions and are both even and positive definite.
The function is constant along the solutions of the nonimpulsive equation
The change in the energy along the solutions of (4.32) is given by
We see that these impulsive perturbations increase the energy. If the energy increases slowly, then we expect the solutions to oscillate. On the other hand, if the energy increases too fast, the solutions become nonoscillatory. Let be a solution of (4.32), and Calculating in terms of we obtain
To simplify the notation, we introduce the function
The function gives the jump in the quantity Note that for and is monotone increasing with respect to and decreasing with respect to
Theorem 4.13 (see [29]).
Assume that there exist a constant and a sequence with such that
holds for every Then every solution of (4.32) is nonoscillatory.
Theorem 4.14 (see [29]).
Assume that there exist a constant and a sequence with and such that for every
holds for every Then every solution of (4.32) is oscillatory.
Proof.
Let be a nontrivial solution of (4.32). It suffices to show that cannot hold on any interval Assume that to the contrary, for Let be defined by where It follows from (4.39) that Hence,
Since and the right side of the above inequality tends to infinity as we have a contradiction.
Now, assume that for every It can be shown that the integral
takes its maximum in at
In the special case we have the following necessary and sufficient condition.
Theorem 4.15 (see [29]).
Assume that Then every solution of (4.32) is nonoscillatory if and only if
Remark 4.16.
Equation (4.32) with was studied in [30].
Finally, we consider the secondorder impulsive differential equation of the following form:
where , are real constants, is a strictly increasing unbounded sequence of real numbers, and are real sequences, , and
All results given in the remainder of this section are from [31].
Theorem 4.17.
Suppose that for any given , there exist intervals , , such that

(a)
for all and for all for which ;

(b)
, , , ; , , , for all
If there exists such that
where
then (4.44) is oscillatory.
Proof.
Suppose that there exists a nonoscillatory solution of (4.44) so that for all for some . Let
It follows that for ,
where dependence is suppressed for clarity.
Define a function by
It is not difficult to see that if , then
Clearly, if , then we have . Thus, with our convention that , (4.51) holds for .
Suppose that for all . Choose and consider the interval . From (b), we see that on and for all for which . Applying (4.51) to the terms in the parenthesis in (4.49) we obtain
where and are defined by (4.46) and (4.47), respectively.
Let . Multiplying (4.52) by and integrating over give
In view of (4.52) and the assumption , employing the integration by parts formula in the last integral we have
We use Lemma 4.1 with
to obtain
which obviously contradicts (4.45).
If is eventually negative then we can consider and reach a similar contradiction. This completes the proof.
Example 4.18.
Consider
where is a positive real number.
Let , , and . For any given we may choose sufficiently large so that . Then conditions (a)(b) are satisfied. It is also easy to see that, for and ,
where and . It follows from Theorem 4.17 that (4.57) is oscillatory if
Note that if there is no impulse then the above integrals are negative, and therefore no conclusion can be drawn.
When , then (4.44) reduces to forced halflinear impulsive equation with damping
Corollary 4.19.
Suppose that for any given , there exist intervals , for which (a)(b) hold.
If there exists such that
then (4.60) is oscillatory.
Taking in (4.44), we have the forced superlinear impulsive equation with damping
Corollary 4.20.
Let . Suppose that for any given , there exist intervals , , such that (a)(b) hold for all .
If there exists such that
then (4.62) is oscillatory.
Let in (4.62). Then we have the forced linear equation:
Corollary 4.21.
Suppose that for any given , there exist intervals , , such that (a)(b) hold for all .
If there exists such that
then (4.64) is oscillatory.
Example 4.22.
Consider
where is a positive real number.
Let . For any , choose sufficiently large so that and set and . Clearly, (a)(b) are satisfied for all . It is easy to see that for and ,
Thus (4.65) holds if
which by Corollary 4.21 is sufficient for oscillation of (4.66).
Note that if the impulses are removed, then (4.66) becomes nonoscillatory with a nonoscillatory solution .
Finally we state a generalization of Theorem 4.17 for a class of more general type impulsive equations. Let , , , , , , and be as above, and consider
where the functions and satisfy
Theorem 4.23.
In addition to conditions of Theorem 4.17, if (4.70) holds then (4.69) is oscillatory.
Example 4.24.
Consider
where
Clearly if we take and , then (4.70) holds with , and . Further, we see that all conditions of Theorem 4.17 are satisfied if and ; see Example 4.18. Therefore we may deduce from Theorem 4.23 that (4.71) is oscillatory if .
4.3. Oscillation of SecondOrder Nonlinear Equations
In this section, we first consider the secondorder nonlinear impulsive differential equations of the following form:
Assume that the following conditions hold.

(i)
and where , and

(ii)
, and there exist positive numbers such that
(4.74)
In most of the investigations about oscillation of nonlinear impulsive differential equations, the following lemma is an important tool.
Lemma 4.25 (see [25]).
Let be a solution of (4.73). Suppose that there exists some such that for If conditions (i) and (ii) are satisfied, and
(iii) holds, then and for where
Theorems 4.26–4.32 are obtained in [25]. For some improvements and/or generalizations, see [32–35].
Theorem 4.26.
Assume that conditions and of Lemma 4.25 hold, and there exists a positive integer such that for If
then every solution of (4.73) is oscillatory.
Proof.
Without loss of generality, we can assume If (4.73) has a nonoscillatory solution we might as well assume From Lemma 4.25, for where Let
Then, Using condition (i) in (4.73), we get for
Using condition (ii) and yield
From the above inequalities, we have
where Taking and we get
By induction, for any natural number we obtain
Since, above inequality and the hypothesis lead to a contradiction. So, every solution of (4.73) oscillatory.
From Theorem 4.26, the following corollary is immediate.
Corollary 4.27.
Assume that conditions of Lemma 4.25 hold and there exists a positive integer such that for If
then every solution of (4.73) is oscillatory.
The proof of the following theorem is similar to that of Theorem 4.26.
Theorem 4.28.
Assume that conditions and of Lemma 4.25 hold and for any If
then every solution of (4.73) is oscillatory.
Corollary 4.29.
Assume that conditions and of Lemma 4.25 hold and for any Suppose that there exist a positive integer and a constant such that
If then every solution of (4.73) is oscillatory.
Example 4.30.
Consider the superlinear equation:
where is a natural number. Since , , and It is easy to see that conditions (i), (ii), and (iii) are satisfied. Moreover
Hence, by Corollary 4.29, we find that every solution of (4.85) is oscillatory. On the other hand, by Theorem 2.6, it follows that (4.85) without impulses is nonoscillatory.
Theorem 4.31.
Assume that conditions (i), (ii), and (iii) of Lemma 4.25 hold, and there exists a positive integer such that for If
then every solution of (4.73) is oscillatory.
Proof.
Without loss of generality, let If (4.1) has a nonoscillatory solution assume By Lemma 4.25, Since we have
It is easy to see that is monotonically nondecreasing in Now (4.73) yields
Hence, from the above inequality and condition (ii), we find that
Generally, for any natural number we have
By (4.89) and (4.91), noting and for any natural number we obtain
Note that and is nondecreasing. Dividing the above inequality by and then integrating from to we get
Since (4.88) holds, the above inequality yields
The above inequality and the hypotheses lead to a contradiction. So, every solution of (4.73) is oscillatory.
The proof of the following theorem is similar to that of Theorem 4.31.
Theorem 4.32.
Assume that conditions of Lemma 4.25 hold, and there exists a positive integer such that for Suppose that for any and
Then, every solution of (4.73) is oscillatory.
In [36], the author studied the secondorder nonlinear impulsive differential equations of the following form:
where and , .
Sufficient conditions are obtained for oscillation of (4.96) by using integral averaging technique. In particular the Philos type oscillation criteria are extended to impulsive differential equations.
It is assumed that

(i)
is a constant;

(ii)
is a strictly increasing unbounded sequence of real numbers; is a real sequence;

(iii)
, ;

(iv)
, with , for and
(4.97)
is satisfied; is a constant.
In order to prove the results the following wellknown inequality is needed [26].
Lemma 4.33.
If , are nonnegative numbers, then
and the equality holds if and only if .
The following theorem is one of the main results of this study.
Theorem 4.34 (see [36]).
Let and . Assume that , satisfy the following conditions.

(i)
for and on .

(ii)
has a continuous and nonpositive partial derivative on with respect to the second variable.

(iii)
One has
(4.99)
If
where , then (4.96) is oscillatory.
Proof.
Let be a nonoscillatory solution of (4.96). We assume that on for some sufficiently large . Define
Differentiating (4.101) and making use of (4.96) and (4.97), we obtain
Replacing by in (4.102) and multiplying the resulting equation by and integrating from to , we get
Integrating by parts and using (4.103), we find
Combining (4.104) and (4.105), we obtain
Using inequality (4.98) with
we find
From (4.106) and (4.108), we obtain
for all . In the above inequality we choose , to get
Thus, it follows that
which contradicts (4.100). This completes the proof.
As a corollary to Theorem 4.34, we have the following result.
Corollary 4.35.
Let condition (4.100) in Theorem 4.34 be replaced by
then (4.96) is oscillatory.
Note that in the special case of halflinear equations, for and , the condition (4.97) is satisfied with .
The proof of the following theorem can be accomplished by using the method developed for the nonimpulsive case and similar arguments employed in the proof of Theorem 4.34.
Theorem 4.36 (see [36]).
Let the functions and be defined as in Theorem 4.34. Moreover, Suppose that
If there exists a function such that
and for every
where , then (4.96) is oscillatory.
4.4. HigherOrder Nonlinear Equations
There are only a very few works concerning the oscillation of higherorder nonlinear impulsive differential equations [37–40].
In [37] authors considered even order impulsive differential equations of the following form
where
Let the following conditions hold.
for for , where is positive and continuous on for
, and there exist positive numbers such that
A function is said to be a solution of (4.116), if (i) ; (ii) for and satisfies ; (iii) is left continuous on and
The first two theorems can be considered as modifications of Theorems 3.43 and 4.26, respectively.
Theorem 4.37 (see [37]).
If conditions and hold, , , and if
then every bounded solution of (4.116) is oscillatory.
Theorem 4.38 (see [37]).
If conditions and hold, and
then every solution of (4.116) is oscillatory.
Theorem 4.39 (see [37]).
If conditions (A) and (B) hold, , , and for any ,
then every solution of (4.116) is oscillatory.
Corollary 4.40.
Assume that conditions (A) and (B) hold, and that , . If
then every solution of (4.116) is oscillatory.
Corollary 4.41.
Assume that conditions (A) and (B) hold, and that there exists a positive number , such that , . If
then every solution of (4.116) is oscillatory.
Example 4.42.
Consider the impulsive differential equation:
where , , , , , , , .
It is easy to verify conditions of Theorem 4.38. So every solution of (4.124) is oscillatory.
Example 4.43.
Consider the impulsive differential equation:
where , , , , , , , .
In this case, it can be show that conditions of Corollary 4.41 are satisfied. Thus, every solution of (4.125) is oscillatory.
In [40], the authors considered the impulsive differential equations with piecewise constant argument of the following form:
where is the set of all positive integers, , and are given positive constants, denotes the set of maximum integers, and for all . It is assumed that

(i)
;

(ii)
for any and all ,
(4.127)

(iii)
there exists such that
(4.128)
Theorem 4.44 (see [40]).
Assume that conditions , , and hold. Moreover, suppose that for any , there exists a such that
where . Then every solution of (4.126) is oscillatory.
Theorem 4.45 (see [40]).
Assume that conditions and hold. Moreover, suppose that for any , there exists a such that
Then every solution of (4.126) is oscillatory.
Example 4.46.
Consider the impulsive differential equation:
It is easy to verify that conditions of Theorem 4.45 are all satisfied. Therefore every solution of (4.131) is oscillatory.
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Acknowledgments
This work was done when the second author was on academic leave, visiting Florida Institute of Technology. The financial support of The Scientific and Technological Research Council of Turkey (TUBITAK) is gratefully acknowledged.
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Agarwal, R., Karakoç, F. & Zafer, A. A Survey on Oscillation of Impulsive Ordinary Differential Equations. Adv Differ Equ 2010, 354841 (2010). https://doi.org/10.1155/2010/354841
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Keywords
 Impulsive Differential Equation
 Oscillatory Solution
 Nonoscillatory Solution
 Oscillation Criterion
 Oscillation Theorem