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پژوهش های ریاضی، جلد ۶، شماره ۳، صفحات ۴۴۱-۴۴۸
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| عنوان فارسی |
تخمین دقیق ضرایب لگاریتمی رده‌ای خاص از توابع تحلیلی |
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| چکیده فارسی مقاله |
فرض کنید ردۀ همۀ توابع تحلیلی و نرمال شده در قرص واحد باشد. برای هر تابع از خانواۀ ضرایب لگاریتمی به صورت زیر تعریف میشوند:
همچنین، زیرردۀ از را بهصورت زیر تعریف میکنیم
که در آن " " رابطۀ تبعیت است. هدف ما در این مقاله تخمین دقیق نامساویها شامل ضرایب لگاریتمی برای توابعی است که به ردۀ تعلق دارند.
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| کلیدواژه‌های فارسی مقاله |
تابع تک‌ارز، ستاره‌واری، تبعیت، ضرایب لگاریتمی، ضرب پیچشی |
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| عنوان انگلیسی |
Sharp Estimates of Logarithmic Coefficients of Certain Class of Analytic Functions |
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| چکیده انگلیسی مقاله |
Introduction
Let be the open unit disc in the complex plane and be the class of all functions of which are analytic and normalized in The subclass of consisting of all univalent functions in is denoted by We say that a function is said to be starlike function if and only if for all We denote by the class of all satrlike functions in If and are two of the functions in then we say that is subordinate to written or if there exists a Schwartz function such that for all Furthermore, if the function is univalent in then we have the following equivalence: Also for and their Hadamard product (or convolution) is defined by The logarithmic coefficients of , denoted by , are defined by These coefficients play an important role for various estimates in the theory of univalent functions. For example, consider the Koebe function where It is easy to see that the above function has logarithmic coefficients where and Also for the function we have and the sharp estimates and hold. We remark that the Fekete-Szego theorem is used. For , the problem seems much harder and no significant upper bounds for when appear to be known. Moreover, the problem of finding the sharp upper bound for for is still open for . The sharp upper bounds for modulus of logarithmic coefficients are known for functions in very few subclasses of . For functions in the class it is easy to prove that for and the equality holds for the Koebe function. The celebrated de Brangeschr('39') inequalities (the former Milin conjecture) for univalent functions state that where with the equality if and only if De Branges used this inequality to prove the celebrated Bieberbach conjecture. Moreover, the de Brangeschr('39') inequalities have also been the source of many other interesting inequalities involving logarithmic coefficients of such as Let denote the class of functions and satisfying the following subordination relation where .
Material and methods
In this paper, first we obtain a subordination relation for the class and by making use of this relation we give two sharp estimates for the logarithmic coefficients of the function
Results and discussion
We obtain two sharp estimates for the logarithmic coefficients of the function
Conclusion
The following conclusions were drawn from this research. - Logarithmic coefficients of the function are estimated.
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| کلیدواژه‌های انگلیسی مقاله |
Univalent functions, Starlikeness, Subordination, Logarithmic coefficients, Hadamard product. |
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| نویسندگان مقاله |
رحیم کارگر | Rahim Kargar
سازمان مرکزی دانشگاه پیام نور، تهران
علی عبادیان | Ali Ebadian
سازمان مرکزی دانشگاه پیام نور، تهران
نادر کنزی | Nader Kanzi
سازمان مرکزی دانشگاه پیام نور، تهران
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| نشانی اینترنتی |
http://mmr.khu.ac.ir/browse.php?a_code=A-10-552-1&slc_lang=fa&sid=1 |
| فایل مقاله |
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| کد مقاله (doi) |
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| زبان مقاله منتشر شده |
fa |
| موضوعات مقاله منتشر شده |
جبر |
| نوع مقاله منتشر شده |
علمی پژوهشی بنیادی |
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