Nonlinear constraint function is undefined at initial point. Fmincon cannot continue.

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Yoon Ho Roh
Yoon Ho Roh 2021-6-9
回答： Shadaab Siddiqie 2021-6-15
I cannot run fmincon because of the error 'barrier, Nonlinear constraint function is undefined at initial point. Fmincon cannot continue.'
Thanks in advance.
Here is my code
Main fmincon function
R = 25;
H = 27;
LB = [2 * R / H + 2 / H, 0.4, 0.4, 0.4, 0.4];
UB = [4 * R / H - 2 / H, 2.5, 2.5, 2.5, 2.5];
x0 = [1, 1, 1, 1, 1];
tol = 1.0e-6;
options = optimset('display', 'iter', 'PlotFcns', 'optimplotfval', 'TolX', tol, 'TolFun', tol, 'TolCon', tol, 'Algorithm', 'interior-point')
[x, fval, exitflag, output] = fmincon(@(x) objective(x,H), x0, [], [], [], [], LB, UB, @(x) constraints(x,H,R), options)
Objective function
function f = objective (x, H)
f = H^2 * (x(1) + x(2)) * (x(3) + 2 * x(4) + x(1));
end
Constraints
function [C, Ceq] = constraints (x, H, R)
C(2) = x(5) - 2 * R / H + 2 / H;
C(3) = x(3) - 4 * R / H + 2 / H;
C(4) = x(2) - 4 * R / H + 2 / H;
C(5) = 5 - 2 * atan (0.5*(x(3) - x(5)) / x(2));
C(1) = x(2)*((467208*x(2)*x(5)^3*x(3) + 152286*x(2)*x(5)^3 - 1401624*x(2)*x(5)^2*x(3)^2 - 456858*x(2)*x(5)^2*x(3) + 1401624*x(2)*x(5)*x(3)^3 + 456858*x(2)*x(5)*x(3)^2 - 467208*x(2)*x(3)^4 - 152286*x(2)*x(3)^3)/(625*x(2)*x(5)^3 - 1875*x(2)*x(5)^2*x(3) + 1875*x(2)*x(5)*x(3)^2 - 625*x(2)*x(3)^3) - ((1875*x(2)^2*x(5)^2*x(3) - 3750*x(2)^2*x(5)*x(3)^2 + 1875*x(2)^2*x(3)^3)*(116802*x(5)^4 - 467208*x(5)^3*x(3) + 700812*x(5)^2*x(3)^2 - 467208*x(5)*x(3)^3 + 116802*x(3)^4))/(625*x(2)*x(5)^3 - 1875*x(2)*x(5)^2*x(3) + 1875*x(2)*x(5)*x(3)^2 - 625*x(2)*x(3)^3)^2) - ((6*(6447*x(2)^3*x(3) + 5000*x(2)^3))/(x(5) - x(3)) + 38682*x(2)^2*x(2))/(625*x(2)^2*x(3)^2 - x(2)*(1250*x(2)*x(3)^2 - 1250*x(2)*x(5)*x(3)) + x(2)^2*(625*x(5)^2 - 1250*x(5)*x(3) + 625*x(3)^2)) + (14166*x(2)*log(- x(2)*x(3) - x(2)*(x(5) - x(3))))/(625*x(5) - 625*x(3)) + (x(2)^2*(116802*x(5)^4 - 467208*x(5)^3*x(3) + 700812*x(5)^2*x(3)^2 - 467208*x(5)*x(3)^3 + 116802*x(3)^4))/(2*(625*x(2)*x(5)^3 - 1875*x(2)*x(5)^2*x(3) + 1875*x(2)*x(5)*x(3)^2 - 625*x(2)*x(3)^3)) - 96 * ((1 - 1.3553 * x(1) + 1.9467 * x(1)^2) * (x(1) + 1)^2 * ((x(3) + 2 * x(4) + x(1) + x(2)) / H))/ x(1)^3
Ceq = [];
end

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回答（1 个）

Shadaab Siddiqie
Shadaab Siddiqie 2021-6-15
From my understanding you are getting an error "Nonlinear constraint function is undefined at initial point". This might be because your function is not defined a the initial point x0 (in your case [1,1,1,1,1]). You can either change your initial value or may be recheck your objective and its constraints again.

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