Error using plot Vectors must be the same lengths when plotting thetap_dot(k) vs. time.

dt= 0.001; % sampling interval [s]
N= ((T_on+T_off)/dt)+1; % how many "snapshots" in time
t= (0:dt:(N-1)*dt); % duration

xdot(1)= 2/2.23694; % initial velocity [m/s]

for k= 1:(N-1)
    if xdot(k)< 10.2771045561311
        thetap_dot(k)= (1/Rt)*GR*xdot(k);
        xddot(k)= ((GR/Rt)*(P/thetap_dot(k)))/(M+2*It/Rt^2);
    else
        thetap_dot(k)= (1/Rt)*GR*xdot(k);
        xddot(k)= ((GR/Rt)*(0/thetap_dot(k) ))/(M+2*It/Rt^2);
    end
    xdot(k+1)= xdot(k)+ xddot(k)*dt;
end

[VBBV]

Change the for loop index as below

for k = 1: N
...
end

Answer 1

[Walter Roberson]

dt= 0.001; % sampling interval [s]
N= ((T_on+T_off)/dt)+1; % how many "snapshots" in time

N will not usually be an integer, even if T_on and T_off are integers. Remember that 0.001 is not exactly representable in binary floating point, so division by 0.001 is not the same thing as multiplication by 1000, and we as outside observers have no reason to expect that T_on and T_off are integer valued.

With N not usually being an exact integer even if 1000*(T_on+T_off) would be an integer, it becomes difficult to predict the length of

t= (0:dt:(N-1)*dt); % duration

Due to round-off in floating point calculations, this could end up one item shorter than it looks like it "should" be.

You should probably define N as an integer using round() and then use

t = (0:N-1)*dt

[Jenna Le]

hello! even with using the round function for defining N and chancing the N value to be 1000*(T_on+T_off) it still is coming up with the same error.

[VBBV]

N = ((T_on+T_off)/dt)+1;
%if mod(N,1) ~= 0
  %N = floor(N) ;
%else
 % N = N;
%end
t = linspace(0,ceil((N-1)*dt),floor(N));
for k = 1:length(t)
...
end

figure (1)
plot(t,xdot*2.23694,'linewidth',2);
figure (2)
plot(t,((thetap_dot)/(2*pi/60)),'linewidth',2);

Use floor or ceil functions after checking using mod operation

[Walter Roberson]

If mod(N,0) == 0 then floor(N) is the same as N, so you do not need to test with mod()