What is wrong with my code?

Question

Khoirunnisa' Irodatillah 2019-3-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/448193-what-is-wrong-with-my-code

评论： Walter Roberson 2019-3-5

function y = slider(x,x2)
x0 = [3;60];
L2 = 2;
L1 = 4;
x2= 50;
y = [L2*cosd(x2) - x(1)*cosd(x(2)) - L1; 
    L2*sind(x2) - x(1)*sind(x(2))];
end

>> x_full = fsolve(@slider,x0);

>> Rao4 = x_full(1)

Rao4 =

-3.116953357712931

>> theta4 = x_full(2)

theta4 =

-29.441463984624214

It is a equation position for slide crank. The answer for Rao4 should be positive and theta 4 should be around 50 degrees, I try it many times but I don't know what is wrong. I checked with my friend's code, it's the same but still, we have different result. Thank you for your help.

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Answer 1

Walter Roberson 2019-3-4

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https://ww2.mathworks.cn/matlabcentral/answers/448193-what-is-wrong-with-my-code#answer_363796

Your equation has an infinite number of solutions because of the trig, and has two basic forms. You are getting the primary solution to one of the basic forms. If you were to use different x0 you might end up with a different solution.

However, none of the infinite solutions has x(2) near 50 degrees: one of the solutions has an x(2) near 150.56 degrees though. The x(2) values are basically 180 degrees apart from that -29.4 that you produced.