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单词 ProofOfCaratheodorysTheorem
释义

proof of Carathéodory’s theorem


The convex hull of P consists precisely of the points that can be written as convex combination of finitely many number points in P. Suppose that p is a convex combination of n points in P, for some integer n,

p=α1x1+α2x2++αnxn

where α1++αn=1 and x1,,xnP. If nd+1, then it is already in the required form.

If n>d+1, the n-1 points x2-x1, x3-x1,,xn-x1 are linearly dependent. Let βi, i=2,3,,n, be real numbers, which are not all zero, such that

i=2nβi(xi-x1)=0.

So, there are n constants γ1,γn, not all equal to zero, such that

i=1nγixi=0,

and

i=1nγi=0.

Let be a subset of indices defined as

{i{1,2,,n}:γi>0}.

Since i=1nγi=0, the subset is not empty. Define

a=maxiIαi/γi.

Then we have

p=i=1n(αi-aγi)xi,

which is a convex combination with at least one zero coefficient. Therefore, we can assume that p can be written as a convex combination of n-1 points in P, whenever n>d+1.

After repeating the above process several times, we can express p as a convex combination of at most d+1 points in P.

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更新时间:2025/5/5 4:15:22