For a concave function f(x)>=0, N is a positive integer, then 1/(N+1) sum_(j=1)^N f(n)/f(N) increases in N.

robbbiehu

robbbiehu

Answered question

2022-10-26

For a concave function f ( x ) 0, N is a positive integer, then
1 N + 1 n = 0 N f ( n ) f ( N )
increases in N.Let f:R2→R be a continuos concave function which is continuously differentiable in the first variable. Is it true that

Answer & Explanation

plomet6a

plomet6a

Beginner2022-10-27Added 20 answers

Counterexample:
f ( x ) = x + 1 .
1 N + 1 n = 0 N f ( n ) f ( N ) = 1 2 ( 1 + 2 2 ) 0.853553... ;
1 N + 1 n = 0 N f ( n ) f ( N ) = 1 3 ( 1 + 2 + 3 3 ) 0.797948... ;
1 N + 1 n = 0 N f ( n ) f ( N ) = 1 4 ( 1 + 2 + 3 + 2 2 ) 0.768283... ;

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