Find argmin of function with two input variables

14 ビュー (過去 30 日間)
ABCDEFG HIJKLMN
ABCDEFG HIJKLMN 2021 年 11 月 29 日
コメント済み: Matt J 2021 年 11 月 29 日
Hello, I want to find the arguments of a function La(x1, x2) that minimize this function by calculating the diff of the function in order of x1 and x2, equal to 0 and solving them. MATLAB keeps returning Empty sym: 0-by-1 and I don't understand why. Any help?
Also, if the derivative of the function in order of one of the variables was equal to 1, and then MATLAB tried to calculate 1 == 0, what would it return?
syms x1 x2
assume(x1 > 0.1)
assumeAlso(x1 < 2.0)
assumeAlso(x2 > 0.1)
assumeAlso(x2 < 2.5)
La(x1, x2) = x1^2 + x1 + x2^2 + 5*x2;
eqn1 = [diff(La, x1)==0];
solx1 = solve(eqn1, x1);
eqn2 = [diff(La, x2)==0];
solx2 = solve(eqn2, x2);

採用された回答

Matt J
Matt J 2021 年 11 月 29 日
編集済み: Matt J 2021 年 11 月 29 日
MATLAB keeps returning Empty sym: 0-by-1 and I don't understand why. Any help?
The solution to diff(La,x1)==0 is x1 = -0.5, which does not satisfy your assumption x1>0.1
and then MATLAB tried to calculate 1 == 0,
It would return no solution, as it should.
syms x
solve(diff(x)==0,x)
ans = Empty sym: 0-by-1
  5 件のコメント
Matt J
Matt J 2021 年 11 月 29 日
Your function is additively separable in this example, so the terms dependent on x2 can be minimized independently of x1.
fminbnd(@(x2) x2^2+5*x2, 0.1,2.5)
ans = 0.1001
If you have to do deal with non-separable functions, you can use fmincon().

サインインしてコメントする。

その他の回答 (0 件)

製品


リリース

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by