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Problem with nonlinear solver fsolve??

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ghazal mohamed
ghazal mohamed 2018-1-8
关闭： MATLAB Answer Bot 2021-8-20
Hi everyone,
I try to solve
g=@(x)((0.01783926*sin(0.02077086*x)/7155831.61*x)-1.7519952539)
using fsolve toolbox with this options:
options=optimoptions('fsolve','algorithm','Levenberg-Marquardt','Display','off');
but it returns x0 that i passed in parameter see this examples:
>> fsolve(g,0.1,options)
ans =
0.1000
>>fsolve(g,222,options)
ans =
222.0000
fsolve(g,pi,options)
ans =
3.1416
how i can choose the x0 to get a correcte solution?
thanks
  2 个评论
Torsten
Torsten 2018-1-8
Plot your function and you'll find the reason.
Best wishes
Torsten.

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回答（1 个）

John D'Errico
John D'Errico 2018-1-8
Note my use of .* in there, to allow vectorized input.
g=@(x)((0.01783926*sin(0.02077086*x)/7155831.61.*x)-1.7519952539)
ezplot(g,[0 5000])
grid on
Se that your function pretty much never crosses zero. Although, if I allow it to go out much further, it could, since the swings oscillate in size proportionally with x.
So I think you have a problem in your function definition.
  1 个评论
ghazal mohamed
ghazal mohamed 2018-1-9
Hi john, thank you for your reply, yes the problem is with the function's expression.

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