我用fsolve算非线性方程组出错，求大神指教。

function F=answer(x)

Ya=-300;Yb=300;Yc=-500;Zc=-450;Yd=500;Zd=-450;Theta=8;

F=[(x(1)-Ya)^2+x(2)^2-((Yc-Ya)^2+Zc^2);(x(3)-Yb)^2+x(4)^2-((Yd-Yb)^2+Zd^2);(x(1)-x(3))^2+(x(2)-x(4))^2-((Yc-Yd)^2+(Zc-Zd)^2);(x(2)-x(4))/(x(1)-x(3))-(tan(180*Theta/pi))];

end

x0=[1;2;3]

options=optimset('Display','iter');

[x,fval]=fsolve(@answer,x0,options)

Attempted to access x(4); index out of bounds because numel(x)=3.

Error in answer (line 3)

F=[(x(1)-Ya)^2+x(2)^2-((Yc-Ya)^2+Zc^2);(x(3)-Yb)^2+x(4)^2-((Yd-Yb)^2+Zd^2);(x(1)-x(3))^2+(x(2)-x(4))^2-((Yc-Yd)^2+(Zc-Zd)^2);(x(2)-x(4))/(x(1)-x(3))-(tan(180*Theta/pi))];

Error in fsolve (line 218)

fuser = feval(funfcn{3},x,varargin{:});

Caused by:

Failure in initial user-supplied objective function evaluation. FSOLVE cannot continue.

如题，不知错误在哪里。。谢谢！

Answer 1

[tilojej]

方程中有4个未知数，那你初值对应应该给4个：

function main
x0=[1;2;3;41111]
options=optimset('Display','iter');
[x,fval]=fsolve(@answer,x0,options)
end

function F=answer(x)
Ya=-300;Yb=300;Yc=-500;Zc=-450;Yd=500;Zd=-450;Theta=8;
F=[(x(1)-Ya)^2+x(2)^2-((Yc-Ya)^2+Zc^2);(x(3)-Yb)^2+x(4)^2-((Yd-Yb)^2+Zd^2);(x(1)-x(3))^2+(x(2)-x(4))^2-((Yc-Yd)^2+(Zc-Zd)^2);(x(2)-x(4))/(x(1)-x(3))-(tan(180*Theta/pi))];
end