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5.1. THE ND-SYSTEM 57<br />

Figure 5.2: Time instants <strong>to</strong> compute the action of A T p 1<br />

the values along the (finite) diagonals for which t 1 + t 2 is constant, for increasing<br />

values of this constant.<br />

One last remark concerns the computation of all the coordinates of a stationary<br />

point from the eigenvec<strong>to</strong>r of a single matrix such as A T x 1<br />

. Note that if v denotes an<br />

eigenvec<strong>to</strong>r of the matrix A T x 1<br />

corresponding <strong>to</strong> an eigenvalue ξ 1 , then the vec<strong>to</strong>r v =<br />

(y 0,0 ,y 1,0 ,y 2,0 ,y 0,1 ,y 1,1 ,y 2,1 ,y 0,2 ,y 1,2 ,y 2,2 ) T , and the vec<strong>to</strong>r A T x 1<br />

v =(y 1,0 ,y 2,0 ,y 3,0 ,<br />

y 1,1 ,y 2,1 ,y 3,1 ,y 1,2 ,y 2,2 ,y 3,2 ) T differ by the scalar fac<strong>to</strong>r ξ 1 . This implies that the<br />

columns of the matrix ⎛<br />

y 0,0 y 1,0 y 2,0 y 3,0<br />

⎜ y 0,1 y 1,1 y 2,1 y 3,1 ⎟<br />

(5.17)<br />

⎝<br />

⎠<br />

y 0,2 y 1,2 y 2,2 y 3,2<br />

⎞<br />

are all dependent: each column is equal <strong>to</strong> ξ 1 times its preceding column. If the<br />

vec<strong>to</strong>r v also happens <strong>to</strong> be an eigenvec<strong>to</strong>r of the matrix A T x 2<br />

corresponding <strong>to</strong> an<br />

eigenvalue ξ 2 (the theory of the previous chapter makes clear that such vec<strong>to</strong>rs v<br />

always exist and in case of distinct eigenvalues of A x1 will au<strong>to</strong>matically have this<br />

property) then the rows of the matrix exhibit a similar pattern: each row is equal

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