error occurs when using fsolve

Question

desword jacky 2015-9-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/244658-error-occurs-when-using-fsolve

回答： Kevin Doherty 2015-9-23

This is my function

function F = fun(x)     
dfdx(1) = - 9007199254740992/(93649721522480385*(x(1) - 1)) - 36028797018963968/(93649721522480385*x(1));
dfdx(2) = - 72057594037927936/(468248607612401925*(x(2) - 1)) - 36028797018963968/(156082869204133975*x(2));
dfdx(3) = (- 31525197391593472/(468248607612401925*(x(3) - 1)) - 4503599627370496/(156082869204133975*x(3)));

after execute the "fsolve" function, error occurs

>> y = fsolve('fun',[0.000001 0.000001])
Error using feval
Output argument "F" (and maybe others) not assigned during call to "C:\Program
Files\MATLAB\R2013a\bin\fun.m>fun".
Error in fsolve (line 218)
            fuser = feval(funfcn{3},x,varargin{:});
Caused by:
    Failure in initial user-supplied objective function evaluation. FSOLVE cannot continue.

Is it means that fsolve can not solve this function ? Thanks a lot!

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Answer 1

Kevin Doherty 2015-9-23

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/244658-error-occurs-when-using-fsolve#answer_193456

Your error says "Output argument F not assigned". Your function, "fun" is defined as having an output, which you call F. However, F is not defined anywhere within fun. You have defined dfdx though. This is what you are trying to solve, so this must be your output argument.

Also, you have another problem. Your input vector, x, has three components. However, your initial guess for it, [0.000001, 0.000001], only has two.