Unable to perform assignment because the left and right sides have a different number of elements.

problem solved. Thanks

[Jon]

Hi,

I'm glad you solved your problem, but it looks like you deleted the text of your original post. It would be good to leave it up in case other people have a similar problem. Also, it leaves the answer I posted hanging without any context. If you still have a copy of it it would be good to put it back. If my answer below solved your problem please accept it.

Answer 1

[Jon]

I'm sorry I don't have time to fully understand your code, from a quick look I think your problem may be in your function at line 98

y2_2nd = @(t,q,dqdt) (Q_q-C_q.*dqdt.^2)./J_q;

along with the later line 102

k_12 = y2_2nd(t(i),q(i),dqdt(i));

Your function contains the terms Q_q and C_q both of which are vectors. This means that y2_2nd returns a vector and as result k_12 is also a vector. I'm thinking that you want k_12 to be a scalar constant.

Similar problems then occur in the later terms lines 103-108 so that finally at line 110 you are trying to assign a scalar, q(i+1) to a vector, since, k_21, k_31, and k_41 are all vectors so the right hand side of line 110 evaluates to a vector.

If you don't know how to use it already I would suggest learning how to use the MATLAB debugger, which is helpful for stepping through the code and examining variables as the calculation progresses https://www.mathworks.com/help/matlab/matlab_prog/debugging-process-and-features.html