{"title":"Monotonic solutions of a composite functional equation","authors":"Soichi Ikeda","doi":"10.1007/s00010-026-01330-5","DOIUrl":null,"url":null,"abstract":"<div><p>Chao first considered the composite functional equation </p><div><div><span>$$\\begin{aligned} f(x + 2f(y)) = f(x) + y + f(y) \\quad (x, y \\in \\mathbb {R}), \\end{aligned}$$</span></div></div><p>where <span>\\(f: \\mathbb {R} \\rightarrow \\mathbb {R}\\)</span>. This equation was studied by several mathematicians. In this paper, we study the monotonic solutions of the composite functional equation </p><div><div><span>$$\\begin{aligned} f(xyf(y)) = f(x) y f(y) \\quad (x, y \\in \\mathbb {R}), \\end{aligned}$$</span></div></div><p>where <span>\\(f: \\mathbb {R} \\rightarrow \\mathbb {R}\\)</span>. This equation is similar to Chao’s equation.</p></div>","PeriodicalId":55611,"journal":{"name":"Aequationes Mathematicae","volume":"100 6","pages":""},"PeriodicalIF":0.9000,"publicationDate":"2026-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00010-026-01330-5.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Aequationes Mathematicae","FirstCategoryId":"100","ListUrlMain":"https://link.springer.com/article/10.1007/s00010-026-01330-5","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0
Abstract
Chao first considered the composite functional equation
$$\begin{aligned} f(x + 2f(y)) = f(x) + y + f(y) \quad (x, y \in \mathbb {R}), \end{aligned}$$
where \(f: \mathbb {R} \rightarrow \mathbb {R}\). This equation was studied by several mathematicians. In this paper, we study the monotonic solutions of the composite functional equation
$$\begin{aligned} f(xyf(y)) = f(x) y f(y) \quad (x, y \in \mathbb {R}), \end{aligned}$$
where \(f: \mathbb {R} \rightarrow \mathbb {R}\). This equation is similar to Chao’s equation.
期刊介绍:
aequationes mathematicae is an international journal of pure and applied mathematics, which emphasizes functional equations, dynamical systems, iteration theory, combinatorics, and geometry. The journal publishes research papers, reports of meetings, and bibliographies. High quality survey articles are an especially welcome feature. In addition, summaries of recent developments and research in the field are published rapidly.