Thank you very much for your response

I am trying to find numerical solution.

In Matlab:

+12 equations with 12 unknowns from x1 to x12 (dt=0.01 known)

f1 = x1*x11 + x2*x12 + x5*x9 + x6*x10;

f2 = x3*x11 + x4*x12 + x7*x9 + x8*x10;

f3 = x1*x11 + 0.0019*dt*x1 + x2*x12 + 0.8960*dt*x2 + x5*x9 + dt*x5*x11 + 0.001*dt^2*x5 + x6*x10 + dt*x6*x12 + 0.4480*dt^2*x6 + 0.3828;

f4 = x3*x11 + 0.0019*dt*x3 + x4*x12 + 0.8960*dt*x4 + x7*x9 + dt*x7*x11 + 0.001*dt^2*x7 + x8*x10 + dt*x8*x12 + 0.4480*dt^2*x8 - 0.3844;

f5 = x1*x11 + 0.0080*dt*x1 + x2*x12 + 1.8396*dt*x2 + x5*x9 + 2*dt*x5*x11 + 0.0059*dt^2*x5 + x6*x10 + 2*dt*x6*x12 + 1.8158*dt^2*x6 + 0.8342;

f6 = x3*x11 + 0.0080*dt*x3 + x4*x12 + 1.8396*dt*x4 + x7*x9 + 2*dt*x7*x11 + 0.0059*dt^2*x7 + x8*x10 + 2*dt*x8*x12 + 1.8158*dt^2*x8 - 0.8412;

f7 = x1*x11 + 0.0189*dt*x1 + x2*x12 + 2.8060*dt*x2 + x5*x9 + 3*dt*x5*x11 + 0.0193*dt^2*x5 + x6*x10 + 3*dt*x6*x12 + 4.1386*dt^2*x6 + 1.3449;

f8 = x3*x11 + 0.0189*dt*x3 + x4*x12 + 2.8060*dt*x4 + x7*x9 + 3*dt*x7*x11 + 0.0193*dt^2*x7 + x8*x10 + 3*dt*x8*x12 + 4.1386*dt^2*x8 - 1.3620;

f9 = x1*x11 + 0.0351*dt*x1 + x2*x12 + 3.7696*dt*x2 + x5*x9 + 4*dt*x5*x11 + 0.0463*dt^2*x5 + x6*x10 + 4*dt*x6*x12 + 7.4264*dt^2*x6 + 1.9038;

f10 = x3*x11 + 0.0351*dt*x3 + x4*x12 + 3.7696*dt*x4 + x7*x9 + 4*dt*x7*x11 + 0.0463*dt^2*x7 + x8*x10 + 4*dt*x8*x12 + 7.4264*dt^2*x8 - 1.9365;

f11 = x1*x11 + 0.0571*dt*x1 + x2*x12 + 4.7050*dt*x2 + x5*x9 + 5*dt*x5*x11 + 0.0924*dt^2*x5 + x6*x10 + 5*dt*x6*x12 + 11.6637*dt^2*x6 + 2.4984;

f12 = x3*x11 + 0.0571*dt*x3 + x4*x12 + 4.7050*dt*x4 + x7*x9 + 5*dt*x7*x11 + 0.0924*dt^2*x7 + x8*x10 + 5*dt*x8*x12 + 11.6637*dt^2*x8 - 2.5533;

when using "solve" function in Matlab, no code is needed

when using the Secant method, the code is as follows

dt=1e-2;

% initial values for variables

varc=[120,-40,-40,40]; vark=[1600,-600,-600,600]; var=[];

for i =1:25

[var]=[var;[awgn(varc,20,'measured')],[awgn(vark,20,'measured')],[ 0.01*randn(1,4)], [0.1*randn(1,12)]];

end

k=12;tol=1e-6; ndof=2; ns=1; B=zeros(1,24); B=[B,1]'; neq=ns*k; % (neq is the number of equations)

[A]=A2dofs(var,ndof,dt);

[A]=[A;ones(1,k+1)];

n=zeros(k+1,1); for ii=1:length(n) n(ii)=norm(A(1:neq,ii)); end

xx=var; e1=max(n); % save result for visualization purpose

for jj=1:500

p=A\B;

var_bar=p'*var;

pp=[A2dofs(var_bar,ndof,dt);1];

% Find the column which have maximal norm and replace:

[maxn,Imax]=max(n);

[minn,Imin]=min(n);

var(Imax,

=var_bar;

A(:,Imax)=pp;

n(Imax)=norm(pp(1:neq,1));

err1=norm(var_bar-var(Imin,

);

err2=n(Imax); [e1]=[e1,max(err1,err2)];

iter=jj;

[xx]=[xx;var_bar];

if (err1<tol) & (err2<tol)

break

end

end

Where A2dofs is simply the m-file to evaluate the value of the 12 functions at certain value of x1 to x12.

If possible, pls contact me directly through my email:

g0500479@nus.edu.sg
Thank you very much.