How to use fsolve when solving with trapezoidal method?

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Ilyan Njim 2023-4-26

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https://ww2.mathworks.cn/matlabcentral/answers/1953214-how-to-use-fsolve-when-solving-with-trapezoidal-method

评论： Mannan 2023-8-9

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I need help to begin with the function using trapezoidal method and then solving it with fsolve.

should I use an anonymous function or something else?

I'm trying to get a plot of 6 graphs, is the plot correct or should it be in the for_loop?

here is my code please help!

m1=465;
m2=55;
k1=5350;
k2=13610000;
c1=310;
c2=1250;
v0=[0,0,0,0]';
I=eye(4);
V=[0,0,0,0]';
F_prev=[0;0;0;(k2*hfunc(0)+c2*hdotfunc(0))/m2];
A=[0,0,1,0;0,0,0,1;(-k1/m1),(k1/m1),(-c1/m1),(c1/m1);(k1/m2),((-k1-k2)/(m2)),(c1/m2),((-c1-c2)/(m2))];
% Define function to solve for
imptrap = @(V,V_next) (V(i)-V(i+1)+ (s/2)*(A*V(i)+F_prev+A*V_next+F));
l=max(eig(A));
hl=(-2*real(l))/(((real(l)).^2)+(imag(l)).^2);
Vvec=[];
for j=1:3
    s=hl*(10^(j-1));
    rnditc=round(1/s);
    %U=zeros(4,rnditc);
    
    t=0;
   
    tvec=t;
    F_prev=[0;0;0;(k2*hfunc(t)+c2*hdotfunc(t))/m2];
    for i=1:rnditc
        %Beräknar F för varje t
        F=[0;0;0;(k2*hfunc(t)+c2*hdotfunc(t))/m2];
        %Euler bakåt
        V= fsolve(imptrap, v0);        
        F_prev = F;
        %V = V_next;
        t=t+s;
        Vvec = vertcat(Vvec, V);
        tvec=[tvec t];
    end
end
plot(tvec(:),Vvec(1,:));
hold on 
plot(tvec(:),Vvec(2,:));
hold on 
xlabel("Tid")
ylabel("Utslag")
xlim([0 1])
hold on