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Let Wi(i=0,1,2,...) be i.i.d. random variables following a standard normal distribution N(0,1). For a continuously differentiable function f:[0,1]R, consider the following random variable:

Xn=i=0n1n(f(i+1n)f(in))Wi

Well, the equation itself looks a lot like gaussian quadrature, so I thought maybe this has something to do with it...

EDIT1:

I just realized that this is essentially a sum of random variables following a standard normal distribution, so the sum also follows a standard normal distribution.

Then, we have E[Xn]=0,Var[Xn]=i=0n1n(f(i+1n)f(in))2

So,Xn converges in distribution to a normal distribution, due to the central limit theorem?

EDIT 2: Thank you to those who have commented. I now have for n E[Xn]=0,Var[Xn]01f(x)2dx.

Then Xn would intuitively converge to a normal distribution with the above average and variance, but how can I show this more rigorously?

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By the mean-value theorem,

1ni=0n1(f((i+1)/n)f(i/n)1/n)2=1ni=0n1(f(xn,i))2,
where xn,i[i/n,(i+1)/n]. The RHS converges to V01(f(x))2dx and, therefore,

φXn(t)=exp(t22×1ni=0n1(f((i+1)/n)f(i/n)1/n)2)et2V2,
which is the ch.f of a zero-mean normal random variable with variance V.

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