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I have sequences u=(u_1,...,u_N) and v=(v_1,...,v_N) of complex numbers. The indices are "circular", that is, they are interpreted mod N. Is there a Matlab command that gives the vector w, where w_r = u_{1+r}v_1 + u_{2+r}v_2 + ... u_{N+r}v_N? All the Matlab functions I've looked at give a vector of length 2N1, instead of a vector of length N. I suppose I could just take u twice over, and pad v with zeros, but then conv or whatever will do unnecessary work. In this application efficiency is important. 
"David Epstein" <David.Epstein.spam@remove.warwick.ac.uk> wrote in message <kb1e2o$bj1$1@newscl01ah.mathworks.com>... 
"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <kb1ih7$pcf$1@newscl01ah.mathworks.com>... 
"David Epstein" <David.Epstein.spam@remove.warwick.ac.uk> wrote in message <kb1lkl$61t$1@newscl01ah.mathworks.com>... 
"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <kb1n7a$bdq$1@newscl01ah.mathworks.com>... 
"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <kb1ih7$pcf$1@newscl01ah.mathworks.com>... 
"Matt J" wrote in message <kb3qlb$650$1@newscl01ah.mathworks.com>... 
"Matt J" wrote in message <kb3qlb$650$1@newscl01ah.mathworks.com>... 
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