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

Lagrange multipliers method?

  1. Nov 28, 2015 #1
    upload_2015-11-29_1-56-39.png

    regarding question number 10, we have h = f + λg where g is the constraint (the ellipsoid) and f is the function we need to maximize or minimize (the rectangular parallelpiped volume),
    now my question : is it right that f is 8xyz ? i mean if we take f to be xyz not 8xyz and solved till we got the value of xyz, the resulting value is a maximized rectangular parallelpiped in the ellipsoid in one octan only, i mean: to get the whole maximized volume we need multiply by 8, is this right ?
     
  2. jcsd
  3. Nov 28, 2015 #2

    andrewkirk

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes I suspect they want you to take f(x,y,z)=8xyz. Solving for that would give you the largest rectangular parallelpiped whose edges are parallel to the x, y and z axes. Solving the problem without that constraint in italics would I expect be very messy, since you'd have to allow for all possible rotations of the shape in 3D. Fortunately, I expect that the largest such shape is one that obeys that constraint anyway, although the proof of that is not immediately obvious. Since the problem would be so messy without assuming that, I expect they want you to assume it (or, more likely, they never even thought of that complication).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Lagrange multipliers method?
  1. Lagrange Multipliers (Replies: 10)

  2. Lagrange multiplier (Replies: 1)

  3. Lagrange multiplier (Replies: 6)

Loading...