How to solve non-linear equations having modulus expression?

Question

Anuj Kumar Sahoo 2020-12-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/677483-how-to-solve-non-linear-equations-having-modulus-expression

评论： Anuj Kumar Sahoo 2020-12-8

Hi

I am trying to solve a set of non-linear equations with the final expression in the form of:

power=(abs(non-linear equation))^2;

My system is such that I only have access to the value after modulus of the expression. Therefore, I can not solve the expression by comparing the real and imaginary part.

Is there any way to solve this problem in matlab?

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

Ameer Hamza 2020-12-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/677483-how-to-solve-non-linear-equations-having-modulus-expression#answer_564878

See lsqnolin(): https://www.mathworks.com/help/optim/ug/lsqnonlin.html.

Or fmincon(): https://www.mathworks.com/help/optim/ug/fmincon.html for a more general solution.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Anuj Kumar Sahoo 2020-12-4

Hi Ameer

lsqnonlin() and fmincon() are working perfectly as long as I am comparing the real and imaginary part of the expression, before taking the modulus. Unfortunately, in practice I only have access to the power term i.e. (mod(expression))^2. For which I am facing problem.

FYI: I have also tried expressing

abs(a)^2 == a.*conj(a)

But it didn't work as well.:(

请先登录，再进行评论。

Answer 2

Alan Weiss 2020-12-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/677483-how-to-solve-non-linear-equations-having-modulus-expression#answer_565368

As long as you have no bounds, you can use lsqnonlin directly. See Fit a Model to Complex-Valued Data.

Alan Weiss

MATLAB mathematical toolbox documentation

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Anuj Kumar Sahoo 2020-12-8

Hi Alan

Thanks a lot for your suggestion. But I think my problem still is the unavoidable "modulus" expression in my equation which is stopping me from getting correct answer. The link you shared was definitely useful, but didn't serve my purpose in this case. May be this technique will be helpful to me in some other problem.

Regards

请先登录，再进行评论。