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fsolve is not returning the right solutions

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Eliyah Hawila
Eliyah Hawila on 31 Dec 2020
Edited: Matt J on 31 Dec 2020
My code is below. The correct solutions must be (1,0,1) and (-1,0,1) but I keep getting weird answers regardless of my initial guess
function solveeqs()
x0 = [1 1 1];
x = fsolve(@eqns,x0);
x;
eqns(x0)
end
function F = eqns(z)
x1 = z(1);
x2 = z(2);
x3 = z(3);
F(1) = x1 - x1*x2 - x2.^3 + x3*x1.^2 + x3*x2.^2 - x3 - x3*x1 + x3*x1*x2 + x3*x2.^3;
F(2) = x1 - x3*x1 + x3*x2 + 2*x3*x1*x2;
F(3) = 1 + 2*x2.^2 + x3.^2;
end

Answers (2)

Alex Sha
Alex Sha on 31 Dec 2020
Hi, if you think the solutions should be (1,0,1) or (-1,0,1) , then one equation:
F(3) = 1 + 2*x2.^2 + x3.^2;
should be:
F(3) = 1 + 2*x2.^2 - x3.^2;

Matt J
Matt J on 31 Dec 2020
Edited: Matt J on 31 Dec 2020
The solutions you've cited definitely do not solve the equations you've provided,
F=eqns([-1,0,1])
F = 1×3
0 0 2
F=eqns([1,0,1])
F = 1×3
0 0 2
function F = eqns(z)
x1 = z(1);
x2 = z(2);
x3 = z(3);
F(1) = x1 - x1*x2 - x2.^3 + x3*x1.^2 + x3*x2.^2 - x3 - x3*x1 + x3*x1*x2 + x3*x2.^3;
F(2) = x1 - x3*x1 + x3*x2 + 2*x3*x1*x2;
F(3) = 1 + 2*x2.^2 + x3.^2;
end

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