how to transfer expression to myfun using fsolve?

Question

Franziska 2013-1-21

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/59458-how-to-transfer-expression-to-myfun-using-fsolve

Hi, I am trying to solve a system of nonlinear equations. I have the command in a for loop and each time the number of equations changes. So, I decided to create the expressions using 'sprintf' and than go for fsolve.

My function looks now like that:

function P = myfun(start_r)
eval(variables_R)  % includes r1 = r(1); r2 = r(2); etc.
eval(equations)    % includes P(1) = .....r1 + .....r2^2 - .....; P(2) = ...

So, the error message I receive is: "Undefined function or variable 'variables_R'" which is clear as I have to handle it to myfun.m. How to do that? Where to put variables_R in this expression fsolve(@myfun,start_r)?

Thank a lot for your help in advance. F

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

Walter Roberson 2013-1-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/59458-how-to-transfer-expression-to-myfun-using-fsolve#answer_71924

If you have access to the Symbolic Toolbox, consider describing your system in terms of symbolic variables, and then subs() in any constants you have, and then solve() the system. Or if it is too messy for analytic solutions, using the MuPAD numeric::solve routine.

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。

Answer 2

Franziska 2013-1-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/59458-how-to-transfer-expression-to-myfun-using-fsolve#answer_71926

Thanks for the fast response!

I tried solving it with symbolic variables. It is fine for 3 equations, takes more than 2 hours 4 hours for 5.... and my goal is to realize it for about 70 - 100. So, this is not an option.

I have never worked with MuPad. I just checked it out now, but don't see how it might help me. I want to keep the problem in the normal Matlab-routine since the fsolve command it only one line out of more than 1500 in the code.

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。

Answer 3

Franziska 2013-1-22

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/59458-how-to-transfer-expression-to-myfun-using-fsolve#answer_71994

Ok, here is a way to do it. Define the expressions as global variables. This is not a good way, but it works for now. I am still looking for a more intelligent way...