April 2015 Qu 8 - Lagranigan

Discussion in 'CM2' started by s1645544, Apr 2, 2024.

  1. s1645544

    s1645544 Active Member

    Hi - please could I check my understanding is correct

    Below is the equations I am solving:

    W = 0.0016X1^2 + 0.0144x2^2 + 0.0064x3^2 - lambda(0.02x1 + 0.04x2 + 0.03x3 - E) - mu(x1 + x2+ x3 -1)
    (As I have input e.g. 0.04 in my calculations instead of '4' (meaning 4%) as the solution does)

    when I solve this I get
    lambda = 0.648
    mu = -0.01008

    however the answer is
    lambda = 64.8
    mu = -100.8.

    As my answers which are out by different multiples compared to the solution I am not sure if they are correct? I think the reason they are out by different multiples is to do with squaring the standard deviation to get the variance, therefore the difference of '100' changes to a difference of '1000' (because I have constructed my equation as 0.04 and the solution has constructed their equation as '4' (%)?

    Thanks in advance
     
  2. John Potter

    John Potter ActEd Tutor Staff Member

    Yes, this is all fine. You will get different answers depending on the units you use.

    In fact, because the Lagrangian function is a mixture of units, you can get different Lagrangian multipliers (and not just obviously out by factors of 10), I believe depending on your method. But they all end up at the same efficient frontier

    John
     
  3. s1645544

    s1645544 Active Member

    Thank you John! That is very helpful.
     

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