Error: Unexpected MATLAB expression

Can someone help me with this?

g = 9.81;
m = 0.5;
d = 0.05;
A = 12.e-4;
B = 12.e-4;
C = 4.5e-4;
wspin = (1000*2*pi)/60;
theta = 60;

z = [sind(theta) 0 cosd(theta)];
p = [0 1 0];

y = cross(z,p);
x = cross (y,z);
i = x/norm(x);
j = y/norm(y);
k = z/norm(z);
QXx = [i; j; k];
q0 = dcm2quat(QXx);
w0 = [0 0 wspin]';
t0 = 0;
tf = 2;
f0 = [q0; w0];

[t,f] = rkf45(@rates, [t0,tf], f0);

q  = f(:,1:4);
wx = f(:,5);
wy = f(:,6); 
wz = f(:,7);

for m = 1:length(t)
    QXx                      = quat2dcm(q(m,:));
    [prec(m) nut(m) spin(m)] = dcm2angle(QXx);
end

plotit

`````````````````````````````````````````````````````````

function dfdt = rates(t,f)

q  = f(1:4);
wx = f(5);
wy = f(6);
wz = f(7);

q = q/norm(q);

Q = quat2dcm(q);

M = Q*[-m*g*d*Q(3,2)
        m*g*d*Q(3,1)
                  0];
Omega = [ 0    wz  -wy   wx
         -wz   0    wx   wy
          wy  -wx    0   wz
         -wx  -wy  -wz    0];
q_dot = (Omega*q)/2;

wx_dot = (M(1))/A - ((C-B)*wy*wz)/A;
wy_dot = (M(2))/B - ((A-C)*wz*wx)/B;
wz_dot = (M(3))/C - ((B-A)*wx*wy)/C;

dfdt = [q_dot; wx_dot; wy_dot; wz_dot];

end

`````````````````````````````````````````````````````

function plotit

figure(1)

subplot(311)
plot(t, prec)
xlabel('time (s)')
ylabel('precession angle (deg)')
axis([-inf, inf, -inf, inf])
grid

subplot(312)
plot(t, nut)
xlabel('time (s)')
ylabel('nutation angle (deg)')
axis([-inf, inf, -inf, inf])
grid

subplot(313)
plot(t, spin)
xlabel('time (s)')
ylabel('spin angle (deg)')
axis([-inf, inf, -inf, inf])
grid

end

Answer 1

[Walter Roberson]

.m files cannot include any other period in their name. .m files must follow the rules for MATLAB identifiers: they have to start with a letter (A to Z or a to z), after which you can use letters or digits 0 to 9 or the underscore ('_') character. The maximum length excluding the '.m' is 63 characters.

So you could have named your file Ex23.m or Ex_23.m but not Ex.23.m

Answer 2

[Walter Roberson]

The "`````````````````````````````````````````````````````````" are not valid in MATLAB code.

Otherwise... perhaps you should post the complete error, everything in red

[amir azlan]

thanks for your help with the code,it is my first time using this website. as for the coding, do you know how to fix the error?

[Steven Lord]

When I copied your code into the Editor, added % before your "separator" lines, and turned your first block of code into a function I saw no red Code Analyzer messages, which I would have expected from the error you paraphrased in your question's subject. I could not execute your code, however, since you didn't provide rkf45.

I would also advise you NOT to try to change the limits of your axes to -Inf to Inf -- you don't have an infinitely wide or tall monitor.

I second Walter's request -- post the FULL, COMPLETE text of the error message that MATLAB displays when you try to execute this code if you need further assistance.

[amir azlan]

this is the error massage when i executed the MATLAB code

[amir azlan]

this is the rkf45 code

if true
  % code
end
function [tout, yout] = rkf45(ode_function, tspan, y0, tolerance)

 a = [0 1/4 3/8 12/13 1 1/2];
b = [   0             0           0         0           0
       1/4            0           0         0           0
       3/32          9/23         0         0           0
       1932/2197  -7200/2197  7296/2197     0           0
       439/216       -8       3680/513  -854/4104       0
       -8/27          2      -3544/2565  1859/4104   -11/40];
c4 = [25/216  0  1408/2565   2197/4104   -1/5   0  ];
c5 = [16/135  0  6656/12825  28561/56430 -9/50  2/55];

 if nargin < 4
    tol = 1.e-8;
else
    tol = tolerance;
end

t0 = tspan(1);
tf = tspan(2);
t  = t0;
y  = y0;
tout = t;
yout = y';
h  = (tf - t0)/100;

while t < tf
  hmin = 16*eps(t);
  ti   = t;
  yi   = y;

    for i = 1:6
        t_inner = ti + a(i)*h;
        y_inner = yi;
        for j = 1:i-1
            y_inner = y_inner + h*b(i,j)*f(:,j);
        end
        f(:,i) = feval(ode_function, t_inner, y_inner);
    end

    te = h*f*(c4' - c5');

    te_max = max(abs(te));

    ymax = max(abs(y));
    te_allowed = tol*max(ymax,1.0);

    delta = (te_allowed/(te_max + eps))^(1/5);

    if te_max <= te_allowed
        h      = min(h, tf-t);
        t      =  t + h;
        y      =  yi + h*f*c5';
        tout   =  [tout;t];
        yout   =  [yout;y'];
    end

    h = min(delta*h, 4*h);
    if h < hmin
         fprintf(['\n\n Warning: Step size fell below its minimum\n'
                  ' allowable value (%g) at time %g.\n\n'], hmin, t)
         return
    end
end