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In mathematics, the Levi-Civita field, named after Tullio Levi-Civita, is a non-Archimedean ordered field; i.e., a system of numbers containing infinite and infinitesimal quantities. Its members can be constructed as formal series of the form : is the set of rational numbers, and is to be interpreted as a positive infinitesimal. The support of ''a'', i.e., the set of indices of the nonvanishing coefficients must be a left-finite set: for any member of , there are only finitely many members of the set less than it; this restriction is necessary in order to make multiplication and division well defined and unique. The ordering is defined according to dictionary ordering of the list of coefficients, which is equivalent to the assumption that is an infinitesimal. The real numbers are embedded in this field as series in which all of the coefficients vanish except . ==Examples== * is an infinitesimal that is greater than , but less than every positive real number. * is less than , and is also less than for any positive real . * differs infinitesimally from 1. * is greater than , but still less than every positive real number. * is greater than any real number. * is interpreted as . * is a valid member of the field, because the series is to be construed formally, without any consideration of convergence. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Levi-Civita field」の詳細全文を読む スポンサード リンク
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