error in fsolve solving nonlinear equations

Question

Joaquim Monteiro 2015-12-29

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/262010-error-in-fsolve-solving-nonlinear-equations

评论： Walter Roberson 2015-12-29

Hi I'm trying to solve nonlinear equations with the following code:

 F = myfun(x)
 F = [ x(1)-((500+0.85*(((0.711+0.56*15/100+0.73*(15/100)^2)*5.67*10^(-8)*(25+273.15)^4*(1-cos(30*pi/180))/2)-5.67*10^(-8)*(25+273.15)^4))*1.6*0.8*(1-0*2)*1-1.6*((32+6.4*2)*(x(5)-25)));
    x(2)-(2068.5072425+(-20.1259571429)*x(4)+0.0701428571*x(4)^2+(56.5615102375+(-0.0892494524)*x(4)+(-0.0013878571)*x(4)^2)*x(5)+(0.669960831250007+(-0.001477845238096)*x(4)+0.000000357142857*x(4)^2)*x(5)^2);
    x(3)-(373.160515+(-0.7728)*x(4)+0.0378095238*x(4)^2+((-4.03604873)+0.2014116*x(4)+0.0005034286*x(4)^2)*x(5)+((-0.22703617375)+0.003774373809524*x(4)+(-0.000001214285714)*x(4)^2)*x(5)^2);
    x(2)-(70*(x(4)-40));
    x(2)-(x(3)+x(1)-12*(x(4)-20))];

Then I run the follwing:

x0 = [-5; -5];  % Make a starting guess at the solution
options = optimoptions('fsolve','Display','iter'); % Option to display output
[x,fval] = fsolve(@myfun,x0,options) % Call solver

I got the following errors in workspace:

Attempted to access x(5); index out of bounds because numel(x)=2.
Error in myfun (line 2)
F = [
x(1)-((500+0.85*(((0.711+0.56*15/100+0.73*(15/100)^2)*5.67*10^(-8)*(25+273.15)^4*(1-cos(30*pi/180))/2)-5.67*10^(-8)*(25+273.15)^4))*1.6*0.8*(1-0*2)*1-1.6*((32+6.4*2)*(x(5)-25)));
Error in fsolve (line 217)
          fuser = feval(funfcn{3},x,varargin{:});
Error in testes_auxiliares_eqnonlinear_v2 (line 3)
[x,fval] = fsolve(@myfun,x0,options) % Call solver

Can someone help me.

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Answer 1

Alan Weiss 2015-12-29

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/262010-error-in-fsolve-solving-nonlinear-equations#answer_204557

Well, you gave x0 = [-5;5], but your equation has components x(1) through x(5). You either need to have equations involving only x(1) and x(2), or you need to give a five-element initial vector x0.

Alan Weiss

MATLAB mathematical toolbox documentation