How to resolve this error "Unrecognize function or variable" when using fsolve
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I am trying to solve a system of two equations with two varaibles using fsolve in live script. What primarily I want to do is to plot the suface of the output. Below are the
codes for the two scripts I used
First script:
function F = myfun(x)
F = nan(1,2)
F(1) = cosh(b.*a.^2*x(1)^2 + b.*(1-a).^2*x(2)^2)-x(1);
F(2) = cosh(2*b.*a.*(1-a)*x(1)*x(2) + b*.(1-a).^2*x(2)^2)-x(2);
end
Second script;
b = linspace(-2,2,100);
a = linspace(0,1,100);
x0 = [0,0];
x = fsolve(@(x)myfun(x),x0)
Z = a.*x(1) + (1-a).*x(2)
figure
[X,Y] = meshgrid(b,a);
surf(Y,X,Z')
Edit: This is the error message I get
Unrecognized function or variable 'b'.
F(1) = cosh(b*a^2*x(1)^2 + b*(1-a)^2*x(2)^2)-x(1);
x = fsolve(@(x)myfun(x),x0)
fuser = feval(funfcn{3},x,varargin{:});
Caused by:
Failure in initial objective function evaluation. FSOLVE cannot continue.
回答（1 个）
We need to see the full error message copy/pasted, but you may have put the myfun() script in a location where Matlab cannot see it.
Also, you are not passing a and b to myfun(), so myfun() sees them as undefined.
Also, a and b are vectors in your second script, but treated as scalars within myfun, so you need to resolve that as well.
3 个评论
Godwin Osabutey
2021-7-17
Torsten
2021-7-17
You assign a vector of 100 values (cosh(...)) to one scalar element (F(1)).
Same for F(2).
So you will have to call fsolve in a loop 100 times instead.
Matt J
2021-7-17
"Also, a and b are vectors in your second script, but treated as scalars within myfun, so you need to resolve that as well."
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2021-7-17
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