# Toronto Math Forum

## APM346-2012 => APM346 Math => Misc Math => Topic started by: Shu Wang on October 14, 2012, 01:25:44 AM

Title: Lecture Notes 7 -- Ex 3-4
Post by: Shu Wang on October 14, 2012, 01:25:44 AM
sorry for stealing the post; I've got a question regarding to Example 3 and 4 on Lecture 7.
How do you turn the Robin boundary conditions to a function of psi and phi?
Title: Re: Lecture Notes 7 -- Ex 3-4
Post by: Victor Ivrii on October 14, 2012, 04:29:34 AM
sorry for stealing the post; I've got a question regarding to Example 3 and 4 on Lecture 7.
How do you turn the Robin boundary conditions to a function of psi and phi?

It is not stealing but hijacking. Just plug $u=\phi(x+ct)+\psi (x-ct)$ into b.c. and you get a mixture of $\psi'(-ct)$, $\psi(-ct)$ and $\phi'(x+ct)$, $\phi(ct)$. But you know $\phi(ct)$ so you get 1-st order ODE for $\psi$.
Title: Re: Lecture Notes 7 -- Ex 3-4
Post by: Shu Wang on October 14, 2012, 01:31:28 PM
rofl, thanks alot.