MathDB
Miklós Schweitzer 1955- Problem 1

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September 30, 2015
vectorcollege contests

Problem Statement

1. Let a1,a2,,ana_{1}, a_{2}, \dots , a_{n} and b1,b2,,bmb_{1}, b_{2}, \dots , b_{m} be n+mn+m unit vectors in the rr-dimensional Euclidean space Er(n,mr)E_{r} (n,m \leq r); let a1,a2,,ana_{1}, a_{2}, \dots , a_{n} as well as b1,b2,,bmb_{1}, b_{2}, \dots , b_{m} be mutually orthogonal. For any vector xErx \in E_{r}, consider
Tx=i=1nk=1m(x,ai)(ai,bk)bkTx= \sum_{i=1}^{n}\sum_{k=1}^{m}(x,a_{i})(a_{i},b_{k})b_{k}
((a,b)(a,b) denotes the scalar product of aa and bb). Show that the sequence (Tkx)k=0(T^{k}x)^{\infty}_{ k =0}, where T0x=xT^{0} x= x and Tkx=T(Tk1x)T^{k} x = T(T^{k-1}x), is convergent and give a geometrical characterization of how the limit depends on xx. (S. 14)