Aiming to solve function and have one of the variables be a minimum value:

Question

Samy Abisaleh 2020-3-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513241-aiming-to-solve-function-and-have-one-of-the-variables-be-a-minimum-value

评论： Samy Abisaleh 2020-3-27

syms r x
a = 100;
Cp = .70;
b = .50206;
c = 67.402;
d = 1.2;
e = .0277777778; 
eqn = ((100*Cp*x)-(b*x*r*r))/((100*Cp*x)-(c/r)-(b*x*r*r)) == exp(d*acos(e*r));
solx = solve(eqn, x)
[r, fval] = fminsearch(matlabFunction(solx),[1 1])

So I know the last part is wrong. But I am given the "eqn" and I want X to be a minimum value. I am not sure which matlab method I should use to make this happen. I tried to use fminsearch, but it refuses to solve it that way, and I was wondering if theres another method I am unaware of. The r value can be variable and what it ends up being isn't important to me.

Thanks!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Birdman 2020-3-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513241-aiming-to-solve-function-and-have-one-of-the-variables-be-a-minimum-value#answer_422220

在 MATLAB Online 中打开

The key point here is to define solx as a function of r. Try the following code:

syms r x
a = 100;
Cp = .70;
b = .50206;
c = 67.402;
d = 1.2;
e = .0277777778; 
eqn = ((100*Cp*x)-(b*x*r*r))/((100*Cp*x)-(c/r)-(b*x*r*r)) == exp(d*acos(e*r));
solx(r) = solve(eqn, x)
[r, fval] = fminsearch(matlabFunction(solx),1)

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Samy Abisaleh 2020-3-27

This works out perfectly. I believe the mistake I made was in the fminsearch, I needed the final value to be one term and I had it as two. If you look above, you can see at the end I had it as [1 1] and I needed it to be [1].

请先登录，再进行评论。