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Unblocking The Main Thread Solving ANRs and Frozen Frames
On the value distribution of some differential polynomials
1. International Journal of Mathematics and Statistics Invention (IJMSI)
E-ISSN: 2321 – 4767 P-ISSN: 2321 - 4759
www.ijmsi.org Volume 2 Issue 1 || January. 2014 || PP-41-48
On The Value Distribution of Some Differential Polynomials
1,
Subhas.S.Bhoosnurmath, 2, K.S.L.N.Prasad
1,
Department of Mathematics, Karnatak University,
Dharwad-580003-INDIA
2,
Lecturer, Department of Mathematics,
Karnatak Arts College, Dharwad-580001-INDIA
ABSTRACT: We prove a value distribution theorem for meromorphic functions having few poles, which
improves several results of C.C.Yang and others.Also we obtain a generalized form of Clunie’s result.
C. C. Yang [8] has stated the following.
Theorem A Let f(z) be a transcendental meromorphic function with N(r, f) = S(r, f).
If P[f] = f
n
a 1 n 1 f a 2 n 2 f ...... a n
(1)
i f is a homogeneous differential polynomial in f of degree i, then
Tr, Pf nT(r, f ) Sr, f .
Where
each
This result is required at a later stage and we prove the above theorem on the lines of G. P. Barker and A. P.
Singh [1].
Proof we have, P[f] = f
n
a 1 n 1 f a 2 n 2 f ...... a n
an
a f a f
f n 1 1 n 1 2 n 2 ........ n
fn
fn
f
A
A
A
f n 1 1 22 ........ nn
f
f
f
Where A i
(2)
a i n i f
, i 1,2,........
n
f n i
Now, since each n f is a homogeneous differential polynomial in f of degree n,
we have ,
f lo f 1 l1 .......f k
n f
m r, n m r,
fn
f
lk
lk
1 l1
2 l 2
k
r, f f ..... f
= m
f f
f
f 1 l1 f 2 l2 f k lk
.....
m r,
f
f f
O1
= S(r, f), using Milloux‟s theorem [10].
Hence m(r, Ai) = S(r, f), for i = 1,2, . . . ,n.
Now on the circle |z | = r, let
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2. On The Value Distribution of Some Differential Polynomials
A rei Max A1 rei | , | A 2 rei
Then, m (r, A(z)) = S (r, f)
Let
E1 0,2 f rei
and E
2A rei
1
2
,......... A n rei
..,
1
n
(3)
2
be the complementof E1 .
Then, on E1, we have
P[f ] f n 1
A1 A 2
A
2 ......... nn
f
f
f
A
A
A
n
f 1 1 22 .......... nn
..
f
f
f
1 1
1
n
f 1 2 .......... n
..
2
2 2
1 n
n f
2
Hence, on E 1 , log 2
Therefore,
P[f ] log f
n
n
n log f n log 2 log Pf
Therefore, n mr, f
2
1
n log f d
2 0
1
1
n log f d 2 E n log f d
2 E1
1
1
n
n log 2 log P[f ] d 2 E log 2A d
2 E1
2
1
n
log P[f ] d 2 E log A d O1
2 E1
2
m r, P[f ] n mr, A O1
m r, P[f ] Sr, f .
Thus, n m (r, f) m (r, P([f]) + S(r, f).
(4)
Adding n N(r, f) both sides and noting N(r, f) = S(r, f), we get,
nT(r, f) m (r, P[f] ) + S(r, f).
Or n T (r, f) T(r, P(f) ) + S(r, f)
Now, m(r, P[f]) = m r, f
n
(5)
A1f n 1 A 2 f n 2 ........ A n 1f A n , by (2)
m r, f {f n 1 A1 f n 2 ........ A n 1 } m r, A n O (1)
mr, f m r, f n 1 A1 f n 2 ........ A n 1 S r, f
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3. On The Value Distribution of Some Differential Polynomials
Proceeding on induction, we have
mr, Pf n mr, f S(r, f )
Therefore, T(r, P[f] ) n m(r, f) + N(r, P[f] + S(r, f)
But, N(r, P[f] ) = S(r, f), since N (r, f) = S(r, f).
Hence, T(r, P[f] ) n T(r, f ) + S(r, f)
(6)
From (5) and (6) we have the required result.
We wish to prove the following result
Theorem 1 Let f(z) be a transcendental meromorphic function in the plane and Q1 f , Q 2 f be differential
F = P[f] Q1 f Q 2 f ,
polynomials in f satisfying Q1 f 0, Q 2 f 0. Let P(f) be as defined in (1).
If
Then
(7)
n Tr, f N r, 1 N r, P1f
f
Q2
Q2
Q2 1 Nr, f Sr, f
To prove the above theorem, we require the following Lemmas.
Lemma 1 [5]: If Q[f] is a differential polynomial in f with arbitrary meromorphic co-efficients
q j ,1 j n, then
mr, Qf Q m r, f mr, q j Sr, f .
n
j1
*
denote differential polynomials
Lemma 2 [5]: Let Q f and Q f
efficients
If
*
1
*
2
in f with arbitrary meromorphic co-
*
n
q , q ,...,q and q1, q 2 ,...,q s respectively.
P[f]
is
a
homogeneous
Pf Q f Qf where Q n, then
differential
polynomials
in
f
of
degree
n
and
*
n
s
m r, Q * f m r, q * m r, q j Sr, f .
j
j1
j1
This leads to a generalised form of Clunie‟s result.
Lemma 3 [5]: Suppose that M[f] is a monomial in f. If f has a pole at z = z 0 of order m, then z0 is a pole of M[f]
order (m-1) m M .
Lemma 4 [5]: Suppose that Q[f] is a differential polynomial in f. Let z 0 be a pole of f of order m and not a
zero or a pole of the co-efficients of Q[f]. Then z0 is a pole of Q[f] of order atmost m Q Q Q
Proof of Theorem 1
Let us suppose that n Q 2 .
We have
F = P[f] Q1 [f] + Q2 [f]
Therefore,
F
and
F
F
Pf Q1f Q 2 f
F
F
F Pf Q1 f Pf Q1 f Q 2 f
*
Hence, it follows that P f Q f Q f
(8)
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4. On The Value Distribution of Some Differential Polynomials
where
and
Q* f
Pf Q f Q f
F
Q1 f
1
1
F
Pf
(9)
F
Q f Q 2 f Q 2 f .
F
(10)
We have by Lemma 2 and (8),
m r, Q * f Sr, f
Qf
Q * f
Again from (8), P f
Therefore,
(11)
1
mr, Pf m r, Qf m r, *
Q f
(12)
From (10) and Lemma 1, we have
mr, Qf Q 2 mr, f Sr, f .
(13)
By the First Fundamental Theorem and (11), we get
1
1
m r, * Nr, Q* f N r, * Sr, f .
Q f
Q f
*
(14)
Clearly, the poles of Q f occur only from the zeros and poles of F and P[f], the poles of f and the zeros and
poles of the co efficients. Suppose that z0 is a pole of f of order m, but not a zero or a pole of the co-efficients
of P f , Q1 f and Q 2 f .
Hence, from Lemma 4, z0 is a pole of Q[f] of order atmost m Q 2 Q 2 Q 2 1
*
*
If z0 is a pole of Q f , we have from (8), Q f =
Qf
Pf
and hence z0 is a pole of Q f of order atmost m Q 2 Q 2 Q 2 1 mn
*
m( Q 2 n ) (Q 2 Q 2 1)
Also, from (8),
1
Q f
*
Pf
Qf
Hence z0 is a zero of Q*[f] of order atleast mn m Q 2 Q 2 Q 2 1
Thus, we have,
1
1
1
Nr, Q * f N r,
Q * f N r, F N Pf Q2 Q2 1 Nr, f
Q 2 n N r, f Sr, f
we have from (8), P f
(15)
Qf
Q * f
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5. On The Value Distribution of Some Differential Polynomials
Therefore,
Qf
mr, Pf m r,
Q * f
Therefore,
1
mr, Pf mr, Qf m r,
Q * f
Using (14) we have,
1
mr, Pf mr, Qf Nr, Q * f N r,
Q * f Sr, f
Using (4), (13) and (15) we have
1
1
n mr, f Q 2 mr, f N r, N r,
+ Q2 Q2 1 Nr, f
F
Pf
Q 2 n Nr, f Sr, f .
1
Q 2 Q 2 1 Nr, f Sr, f ,
Pf
1
n Tr, f N r, F N r,
Hence, we get ,
Q2
which is the required result.
f n in the above result, we get
F f n Q1 f Q 2 f and
1
n Q2 Tr, f N r, F N r, 1 Q2 Q2 1 Nr, f Sr, f ,
f
Remark (1) Putting P[f] =
which is the result of Zhan Xiaoping [9]
(2) Putting P f a n f
n
a n 1f n 1 .......... . a 0 in the above result,
We get, F P f Q1 f Q 2 f
and
1
n Tr, f N r, F N r, P1f
Q2
Q2
Q2 1 Nr, f Sr, f
which is the result of Hong Xun Yi[4].
Theorem 2 Let
and Q[f]
F f n Qf , where Q[f] is a differential polynomial in f
0.
1
N r, Nr, f
f
If lim
n, then (a, F) 1
r
T, r, f
Proof Let F f
n
where a 0 .
Q[f ]. Putting Q 2 [f ] 0 in the result of Zhan Xiaoping ( remark 1) we have,
1
1
n T(r, f) N r, N r, N(r, f ) S(r, f )
F
f
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6. On The Value Distribution of Some Differential Polynomials
Hence
1
N r ,
F
n lim n
r T ( r , f )
Therefore,
using hypothesis.
1
N r,
F
lim
0
r T(r, f )
1
N r,
F a 0 , for a 0 .
Hence, lim
r
T(r, F)
Therefore, 1 (a, F) 0
Or
(a, F) 1 for a 0 .
Hence the result.
Theorem 3 Let F f Q1 f Q 2 f where Q1[f] and Q2[f] are as defined in Theorem 1.
n
If
1
N r, Q2 Q! 1 Nr, f
f
lim
n Q2
r
Tr, f
and
Q 2 f 0, t hen a, F 1 where a 0.
Proof Let F f Q1 [f ] Q 2 [f ] where Q1 [f ] and Q 2 [f ] are as defined in Theorem .
n
By the result of Zhan Xiaoping [Remark 1], we have
1
1
(n Q 2 ) T(r, f ) N r, N r, (Q 2 Q 2 1) N(r, f ) S(r, f ) .
F
f
1
N r,
F (n ) using hypothesis
Or (n Q ) lim
Q2
2
r T(r, f )
Hence,
1
N r,
Fa 0
lim
r
T( r , f )
which implies 1 (a, F) 0 .
Or
(a, F) 1 for a 0 .
Hence the result.
Theorem 4 Let F P f Q f where P[f] is as defined in (1) and Q[f] is a differential polynomial in f such that
Q[f]
0. If n > 1, then F f and F f
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7. On The Value Distribution of Some Differential Polynomials
Proof Let G = F – a, where a(0) is a finite complex number. Then by Theorem 1,
1
1
n Tr, f N r, N r, Nr, f Sr, f
G
f
Obviously, the zeros and poles of f are that of F respectively
1
1
Nr, f N r, Nr, F Sr, f
f
F
Therefore, N r ,
1
1
N r, Nr, F Sr, f
Fa
F
Thus, n T(r, f) N r ,
3Tr, F Sr, f
Therefore,
Tr, f OTr, F as r
Also,
Tr, F OTr, f as r
Hence the theorem follows.
As an application of Theorem 1, we observe the following .
Theorem 5
No transcendental meromorphic function f can satisfy an equation of the form
a 1 P f Q f a 2 Q f a 3 0 ,where a 1 0, a 3 0, P f is as in (1) and Q[f] is a differential
polynomial in f.
Putting P f f
n
Theorem 6
No transcendental meromorphic function f can satisfy an equation of the form
in the above theorem, we have the following.
a 1f Q[f ] a 2 Q[f ] a 3 0 ,where a 1 0, a 3 0, n is a positive integer and Q[f] is a differential
n
polynomial in f.
This improves our earlier result namely ,
Theorem 7: No transcendental meromorphic function f with N(r, f) = S(r, f) can satisfy an equation of the form
a1 zf z f a 2 zf a 3 z 0
n
(1)
i 1
where
n 1, a 1 z 0 and f M i f a j z M j f is a differential polynomial in f of degree n and
j1
each Mi(f) is a monomial in f.
(Communicated to Indian journal of pure and applied mathematics)
Acknowledgement: The second author is extremely thankful to University Grants Commission for the financial
assistance given in the tenure of which this paper was prepared
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8. On The Value Distribution of Some Differential Polynomials
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[1.]
[2.]
[3.]
[4.]
[5.]
[6.]
[7.]
[8.]
[9.]
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Hayman W. K. (1964) : Meromorphic Functions, Oxford Univ. Press, London.
Hong-Xun Yi (1990) : „On A Result Of Singh‟, Bull. Austral. Math. Soc. Vol. 41 (1990) 417-420.
Hong-Xun Yi (1991) : “On The Value Distribution Of Differential Polynomials”, Jl Of Math. Analysis And Applications 154,
318-328.
Singh A. P. And Dukane S. V. (1989) : Some Notes On Differential Polynomial Proc. Nat. Acad. Sci. India 59 (A), Ii.
Singh A. P. And Rajshree Dhar (1993) : Bull. Cal. Math. Soc. 85, 171-176.
Yang C. C. (1972) : „A Note On Malmquist‟s Theorem On First Order Differential Equations, Ordering Differential Equations‟,
Academic Press, New York.
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722-730.
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