Can't get Newton Rapshon implicit Euler method to work

I think it's because of the jacobian (jg) but I'm not sure how to fix it.

Here's the code:

function [t,y] = mieulernewtonexternoooo(f,jf,intv,y0,N,TOL,nmax)
h=(intv(2)-intv(1))/N;
t=intv(1);
t0=intv(1);
y=y0;
z=y0;
z1=y0;
for i=1:N
    g=@(z)(z1+h*f(t0,z));
    jg=h*jf;
    z=minewton(g,jg,z,t0,TOL,nmax);
    z1=z;
    t0=t0+h;
    y=[y,z];
    t=[t,t0];
end
end

function [z] = minewton(f,jg,y1,t0,TOL,nmax)
diff=TOL*2;
i=0;
y=y1;
while (i<nmax) && (diff>TOL)
    i=i+1;
    z = y - jg \ f(y);
    diff=norm(z-y);
    y=z;
end
end

And example inputs:

intv=[0,10]; 
y0=[2;3]; 
f=@(t,y)[y(2)-2*y(1)+2*sin(t);y(1)-2*y(2)+2*(cos(t)-sin(t))]; 
sol=@(t)[2*exp(-t)+sin(t);2*exp(-t)+cos(t)]; 
N=1000; 
nmax=100; 
TOL=10^-8; 
jf=[-2,1;1,-2]; 

Answer 1

[Torsten]

g should be

g =@(z) z-z1-h*f(t0+h,z)

with Jacobian

jg = eye(2)-h*jf

[iñaki iriondo]

Thank you!!!