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In mathematics, the Pincherle derivative ''T’'' of a linear operator ''T'':K() → K() on the vector space of polynomials in the variable ''x'' over a field K is the commutator of ''T'' with the multiplication by ''x'' in the algebra of endomorphisms End(K()). That is, ''T’'' is another linear operator ''T’'':K() → K() : so that : This concept is named after the Italian mathematician Salvatore Pincherle (1853–1936). == Properties == The Pincherle derivative, like any commutator, is a derivation, meaning it satisfies the sum and products rules: given two linear operators and belonging to # ; # where is the composition of operators ; One also has where is the usual Lie bracket, which follows from the Jacobi identity. The usual derivative, ''D'' = ''d''/''dx'', is an operator on polynomials. By straightforward computation, its Pincherle derivative is : This formula generalizes to : by induction. It proves that the Pincherle derivative of a differential operator : is also a differential operator, so that the Pincherle derivative is a derivation of . The shift operator : can be written as : by the Taylor formula. Its Pincherle derivative is then : In other words, the shift operators are eigenvectors of the Pincherle derivative, whose spectrum is the whole space of scalars . If ''T'' is shift-equivariant, that is, if ''T'' commutes with ''S''''h'' or , then we also have , so that is also shift-equivariant and for the same shift . The "discrete-time delta operator" : is the operator : whose Pincherle derivative is the shift operator . 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「Pincherle derivative」の詳細全文を読む スポンサード リンク
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