Sorting and Global Uniqueness in Two-Good HARA Economies with Many Patience Types
具有多种耐心类型的两种商品HARA经济中的排序与全局唯一性
Andrea Loi, Stefano Matta
AI总结 研究具有异质性耐心类型和共同HARA效用的两种商品纯交换经济中竞争均衡的全局唯一性,通过排序条件将高曲率HARA结果扩展到任意有限类型数,并替代低曲率限制。
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我们研究了具有异质性耐心类型和共同HARA伯努利效用的两种商品纯交换经济中竞争均衡的全局唯一性。本文连接了\citet{GeanakoplosWalsh2018}的CRRA排序结果与\citet{LoiMatta2022,LoiMatta2024}发展的HARA唯一性结果。在CRRA情形下,有序禀赋为唯一性提供了排序机制。在HARA情形下,已知在曲率界限$\gamma\le I/(I-1)$下,对于任意禀赋唯一性成立,其中$I$是耐心类型的数量。对于两种类型,在连接耐心与禀赋构成的单调排序条件下,可以移除曲率限制。本文表明,这种高曲率HARA排序机制并非两种类型情形所特有。我们的主要结果证明了对于任意有限数量的耐心类型和任意$\gamma>1$的全局唯一性。如果类型可以排序,使得更耐心的代理人持有更多第一种商品和更少第二种商品,则均衡价格是全局唯一的。因此,本文将两种类型的高曲率HARA结果扩展到真正的多类型环境,并通过用经济上可解释的排序限制替代低曲率限制,补充了任意禀赋的低曲率结果。在CRRA子情形($b=0$)下,有序禀赋条件与\citet{GeanakoplosWalsh2018}的条件一致,我们的推论恢复了他们的唯一性结果。因此,本文的贡献不在于排序条件本身,而在于其适用范围:通过全局系数比论证,相同的耐心和禀赋构成的排序异质性在移位的HARA情形($b>0$)中排除了多重性,适用于任意有限类型数和任意$\gamma>1$。
We study global uniqueness of competitive equilibrium in two-good pure-exchange economies with heterogeneous impatience types and a common HARA Bernoulli utility. The paper connects the CRRA sorting result of \citet{GeanakoplosWalsh2018} with the line of HARA uniqueness results developed in \citet{LoiMatta2022,LoiMatta2024}. In the CRRA case, ordered endowments provide a sorting mechanism for uniqueness. In the HARA case, uniqueness is known to hold for arbitrary endowments under the curvature bound $γ\le I/(I-1)$, where $I$ is the number of impatience types. For two types, the curvature restriction can be removed under a monotone sorting condition linking patience and endowment composition. The present paper shows that this high-curvature HARA sorting mechanism is not specific to the two-type case. Our main result proves global uniqueness for any finite number of impatience types and any $γ>1$. If types can be ordered so that more patient agents hold weakly more of the first good and weakly less of the second, then the equilibrium price is globally unique. Thus the paper extends the two-type high-curvature HARA result to a genuinely multi-type setting and complements the arbitrary-endowment low-curvature result by replacing the low-curvature restriction with an economically interpretable sorting restriction. In the CRRA subcase ($b=0$), the ordered-endowment condition coincides with that of \citet{GeanakoplosWalsh2018}, and our corollary recovers their uniqueness result. The contribution of the present paper is therefore not the sorting condition itself but its reach: the same ordered heterogeneity in patience and endowment composition rules out multiplicity throughout the shifted HARA case ($b>0$), for any finite number of types and any $γ>1$, through a global coefficient-ratio argument.