Different number of elements error.

I'm trying to model the motion of a pendulum and in my code when I run it to display the different values, I get an error that it is "Unable to perform assignment because the left and right sides have a different number of elements." I haven't seen this error before and I don't understand whats wrong. Does anyone have any ideas?

theta0 = pi/3; g = 9.81; L = 1;

t = 0; tf = 20; dt = 0.005;

nt = (tf-t0)/dt;

t = linspace(t0,tf,nt);

theta = zeros(1,nt);

theta(1) = theta0;

omega = zeros(1,nt);

alpha = zeros(1,nt);

Etotal = zeros(1,nt);

H = L - L*cos(theta);

f = 'Time'; g = 'Omega'; h = 'Theta'; p = 'Alpha'; q = 'Energy';

fprintf('Time \t \t Omega\t \t Theta\t \t Alpha \t \t Energy\n',f, g, h, p, q)

fprintf('%5.2f \t %5.2f \t %5.2f \t %5.2f\n',t,omega,theta,alpha,Etotal);

while t <= 20

t = t + .5;

for k = 1:1:nt-1

omega(k+1) = -g/L*sin(theta(k))*dt + omega(k);

theta(k+1) = omega(k)*dt + theta(k);

alpha(k+1) = (omega(k+1) - omega(k))/dt;

Etotal = g*H + (1/2)*(L*omega)^2;

end

fprintf('%5.2f \t %5.2f \t %5.2f \t %5.2f\n',t,omega,theta,alpha,Etotal);

end

Answer 1

[Star Strider]

Initially, you assign ‘g’ to the gravitational acceleration constant:

theta0 = pi/3; g = 9.81; L = 1;

then here you assign ‘g’ to the character vector ‘'Omega'’ that is a (1x5) character array:

f = 'Time'; g = 'Omega'; h = 'Theta'; p = 'Alpha'; q = 'Energy';

and that causes problems with ‘g’ in this line:

omega(k+1) = -g/L*sin(theta(k))*dt + omega(k);

that then throws the error and stops running the code.

If you correct that, by assigning ‘'Omega'’ to a different variable that is not used elsewhere in your code, you then encounter the problem with ‘^’ here because ‘omega’ is a vector:

Etotal = g*H + (1/2)*(L*omega)^2;

that you can correct by using element-wise exponentiation:

Etotal = g*H + (1/2)*(L*omega).^2;

I will let you do the necessary corrections.

.