Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A question on maximization

  1. Feb 16, 2009 #1
    Hi everyone,

    Suppose f =f(x_1, x_2,...,x_n) be a real-valued, any-time differentiable function. Let each x_i=x_i(u_1, u_2,......,u_{2^n-1}) be a linear function of reall u_i's. Let f=g(u_1, u_2,...,u_{2^n-1}). Then is it right that Max f w.r.t. x_i=Max of g w.r.t. u_i?

    Sorry for the inconvenience of typo. I don't know how to use LateX fonts here.

    Regards,
    NaturePaper
     
  2. jcsd
  3. Feb 16, 2009 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    If a f has a maximum, then that maximum is a specific number. That number is larger than all other values of f no matter what variables you are using. Thus, the answer is "yes". The maximum value of f is independent of the variables.
     
  4. Feb 17, 2009 #3
    @HallsofIvy,

    Does the result will change if all the primary variables x_i's are restricted to have values from an interval [a,b] subset of R?

    Thanks & regards,
    NaturePaper
     
  5. Feb 17, 2009 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    If you also restrict the "u" variables so that the range is the set of permissible x variables, no the result does not change. Of course, if you allow values of the u variables that would give unallowed x values, then maxima might well be different.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook