Error: Unexpected MATLAB expression

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amir azlan
amir azlan 2015-10-14
回答： Walter Roberson 2015-10-14
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

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回答（2 个）

Walter Roberson
Walter Roberson 2015-10-14
.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
Walter Roberson
Walter Roberson 2015-10-14
The "`````````````````````````````````````````````````````````" are not valid in MATLAB code.
Otherwise... perhaps you should post the complete error, everything in red
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amir azlan
amir azlan 2015-10-14
this is the error massage when i executed the MATLAB code
amir azlan
amir azlan 2015-10-14
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

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