Using fsolve to solve nonlinear equations that have user-defined functions

Ke Wu

2021 2 16

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11 次查看（30 天）

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Hi there,

I have a problem using fsolve to solve nonlinear equations that have my own functions. See the code below:

options = optimset('TolFun', 1e-10, 'Display', 'iter', 'MaxFunEvals', 1e10, 'MaxIter', 1e9, 'Algorithm', 'Levenberg-Marquardt');
w=2;
h=1;
l=20;
n=0;
M=0;
E=70*10^9;
I= 1/12*h^3*w;
L=l;
UnknownGuess = rand(1,1);
[Unknowns, fval,exitflag] = fsolve('kkk', UnknownGuess, options,n,M,E,I,L);
P = Unknowns(1);
%%%%%%%%%%%%
function F = kkk(Unknown,n,M,E,I,L)
F(1)=XX([n,Unknown(1),E,I,M,L])+2;
end
%%%%%%%%%%%%
function Y=XX(X)
n=X(1,1);
P=X(1,2);
E=X(1,3);
I=X(1,4);
M=X(1,5);
L=X(1,6);
xmesh = linspace(0,L,100);
solinit = bvpinit(xmesh, @guess);
sol = bvp4c(@bvpfcn, @bcfcn, solinit);
fitobject = fit(sol.x(1,:)',sol.y(1,:)','poly9');
fun1 = @(x) cos(fitobject.p1.*x.^9 + fitobject.p2.*x.^8 + fitobject.p3.*x.^7 + fitobject.p4.*x.^6 + fitobject.p5.*x.^5 + fitobject.p6.*x.^4 + fitobject.p7.*x.^3 + fitobject.p8.*x.^2 + fitobject.p9.*x + fitobject.p10);
Y=integral(fun1,0,L)-L;
function g = guess(x)
g = [sin(x)
     cos(x)];
end
function dydx = bvpfcn(x,y)
dydx = [y(2)
       -P/E/I*(cos(y(1))+n*sin(y(1)))];
end
function res = bcfcn(ya,yb)
res = [ya(1)
       yb(2)-M/(E*I)];
end
end
%%%%%%%%%%%%%
                                        First-Order                    Norm of 
 Iteration  Func-count    Residual       optimality      Lambda           step
     0           2               4               0         0.01
No solution found.
fsolve stopped because the problem appears regular as measured by the gradient,
but the vector of function values is not near zero as measured by the
selected value of the function tolerance.
<stopping criteria details>