# Toronto Math Forum

## APM346-2018S => APM346--Lectures => Topic started by: Jingxuan Zhang on March 17, 2018, 05:34:56 PM

Title: excersice 1, chap 7.3
Post by: Jingxuan Zhang on March 17, 2018, 05:34:56 PM
http://www.math.toronto.edu/courses/apm346h1/20181/PDE-textbook/Chapter7/S7.3.html#sect-7.3.1

Exercise 1 appears quite strange. if $f=0$ on $\Omega=\{\|x\|\geq R\}$ and $u(y)=\int_\Omega G(x,y)f(x)\,dx$, then shouldn't this integral vanish instead of giving that curious form?
Title: Re: excersice 1, chap 7.3
Post by: Victor Ivrii on March 17, 2018, 05:56:10 PM
The formula you refer to is good only for $\Omega=\mathbb{R}^n$. In all other cases it contains integrals over boundary, which are not $0$