why do I get a negative numbers???

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Jonah 2024-11-29，4:55

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https://ww2.mathworks.cn/matlabcentral/answers/2169603-why-do-i-get-a-negative-numbers

评论： Torsten 2024-11-29，20:41

im in the process of programming for a project and i keep getting funtionally impossible answers for the variables everytime i run the code it says it stops prematurely so is that the main problem? it is currently only going through "2.300000e+03" itterations is there a way to increase that?

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Jonah 2024-11-29，5:22

I'm using fsolve, and I'd prefer not to share the code for now at least because it's an assignment that's still open I'm sorry for the trouble. I've been working on it off and on for the past 3-4 days but nothing I do works. I've only just started learning matlab since august and there's still a lot I don't understand.

Jonah 2024-11-29，5:24

As far as what I'm doing to get answers I'm doing

Guess = zeros(1,23) Answers = fsolve(function name, Guess)

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回答（1 个）

Walter Roberson 2024-11-29，5:49

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在 MATLAB Online 中打开

opts = optimoptions('fsolve', 'MaxFunctionEvaluations', 1e6, 'MaxIterations', 1e6);
Guess = linspace(0,.001, 23);
Answers = fsolve(function_name, Guess, opts)

Notice that the guess is set to something non-zero: it is often a bad choice to start the function off at the all-zero vector.

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Walter Roberson 2024-11-29，20:18

在 MATLAB Online 中打开

There is no way to force fsolve to give only positive answers.

Generally speaking, the way around that is to instead use fmincon:

fun2 = @(X) function_name(X).^2;
A = []; b = [];
Aeq = []; beq = [];
lb = zeros(1,length(Guess));
ub = inf(1,length(Guess));
nonlcon = [];
opts = optimoptions('fmincon', 'MaxFunctionEvaluations', 1e6, 'MaxIterations', 1e6);
Answers = fmincon(fun2, Guess, A, b, Aeq, beq, nonlcon, opts);