error at for loop end (courseera course ref. solution- fixed points Lorentz equations)

r=28; sigma=10; b=8/3; 
RelTol=1.e-06; AbsTol=1.e-09;
for nroot=1:3
    if nroot==1, x=1; y=1; z=1; end
    if nroot==2, x=10; y=10; z=10; end
    if nroot==3, x=-10; y=-10; z=-10; end
    error=Inf;
    while error > max(RelTol*max(abs([x,y,z])),AbsTol)
      J=[-sigma, sigma, 0; r-z, -1, -x; y, x, -beta;];
        rhs = -[sigma*(y-x); r*x-y-x*z; x*y-beta*z];
        delta_xyz=rhs/J;
        x = x + delta_xyz(1);
        y = y + delta_xyz(2);
        z = z + delta_xyz(3);
        error=max(abs(delta_xyz));
    end
    xroot(nroot)=x; yroot(nroot)=y; zroot(nroot)=z;
end
roots=[xroot;yroot;zroot];
fprintf('steady-state solution:\n')
fprintf('(x, y, z) = (%2.0f,%2.0f,%2.0f)  \n', roots(:,1));
fprintf('(x, y, z) = (%7.5f,%7.5f,%3.0f)  \n', roots(:,2));
    fprintf('(x, y, z) = (%7.5f,%7.5f,%3.0f)  \n', roots(:,3));

They give the reference solution code as above. When I try to run it I get the error message, which I am really confused with cause this line is just 'end' of for for loop I thought.

"Error in beta (line 19)

y = exp(betaln(z,w));"

many thanks,

Answer 1

[Cris LaPierre]

I wonder if the variable b defined in the first line is supposed to be beta.

However, changing that just led to a new error. If this is truly the reference solution, you should notify the course instructor.