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Vector versions of Prony's algorithm and vector-valued rational approximations

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CS-2018-04. Computer Science Department, Technion - Israel Institute of Technology, Haifa 32000, Israel, (2018)

Abstract

Given the scalar sequencefm1m=0that satisfiesfm=k∑i=1aimi; m= 0;1; : : : ;whereai; i∈Candiare distinct, the algorithm of Prony concerns the determi-nation of theaiand theifrom a finite number of thefm. This algorithm is alsorelated to Pad ́e approximants from the infinite power series∑1j=0fjzj.In this work, we discuss ways of extending Prony’s algorithm to sequences ofvectorsfm1m=0inCNthat satisfyfm=k∑i=1aimi; m= 0;1; : : : ;whereai∈CNandi∈C. Two distinct problems arise depending on whetherthe vectorsaiare linearly independent or not. We consider different approachesthat enable us to determine theaiandifor these two problems, and developsuitable methods. We concentrate especially on extensions that take into accountthe possibility of the components of theaibeing coupled. One of the applicationsconcern the determination of a number of the pairs (i;ai) for which|i|are largest.These applications can be applied to the more general case in whichfm=k∑i=1pi(m)mi; m= 0;1; : : : ;wherepi(m)∈CNare some (vector-valued) polynomials inm, andi∈Caredistinct. Finally, the methods suggested here can be extended to vector sequencesin infinite dimensional spaces in a straightforward manner.

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