1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Please help me understand what this textbook says

  1. Apr 30, 2012 #1
    The attached image is from "Numerical Partial Differential Equations: Conservation Laws and Elliptic Equations" by J.W. Thomas.

    In the beginning the set of test functions, [itex]\phi[/itex] is defined.

    They arrive at equation (9.2.11) by using [itex]\phi(x,T) = \phi(a,t) = \phi(b,t) = 0[/itex].

    Where does this condition come from?


    Attached Files:

    • pg81.jpg
      File size:
      37.4 KB
  2. jcsd
  3. Apr 30, 2012 #2
    I guess, to find out what's going on, I should find out what this set [itex]C_0^1[/itex] is first. It's not defined anywhere else on the book.
  4. Apr 30, 2012 #3


    Staff: Mentor

    The symbol C1 means functions whose first derivative is continuous. From your attached page, I infer that C01 means functions whose first derivatives are continuous, and that are 0 outside some rectangle in R2.
  5. Apr 30, 2012 #4
    Thanks. That helps.

    I guess from that you could say that, if the first derivative of [itex]\phi[/itex] is continuous, then [itex]\phi[/itex] is also continuous, so [itex]\phi = 0[/itex] at the edges of the rectangle? Therefore, [itex]\phi(x,T) = \phi(a,t) = \phi(b,t) = 0[/itex].

    But in that case, why is it not required that [itex]\phi(x,0) = 0[/itex] ?
  6. Apr 30, 2012 #5


    Staff: Mentor

    I don't think you can conclude that, at least based on the document you attached. It looks like there is more to the problem than what you scanned, so perhaps the answer is there.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook