Errort message

[Peter230655]

I am trying to run a simulation with opzy, and I get this error message:

ValueError Traceback (most recent call last) Cell In[9], line 24 22 prob.add_option('max_iter', 3000) # defaul is 3000 23 # Find the optimal solution. ---> 24 solution, info = prob.solve(initial_guess) 25 print('message from optimizer:', info['status_msg']) 26 initial_guess = solution

File c:\Users\Peter\anaconda3\envs\sympy-dev\Lib\site-packages\cyipopt\cython\ipopt_wrapper.pyx:621, in ipopt_wrapper.Problem.solve()

ValueError: Wrong length of x0.

There is no variable x0 im my simulation. What am I doing wrong?

Thanks!!

[moorepants]

I guess your initial guess has the wrong length.

[Peter230655]

Thanks! I I understood from the inverted pendulum exampe, it should be: len(initial_guess) = len(state_symbols) * num_nodes + len(specified_symbols) * num_nodes. If this is correct, then my initial guess seems to have the correct length. stat_symbols = generalized coordinates + generalized speeds specified_symbols = external forces, external torques. Should attach my program here / send it to you?

[tjstienstra]

Are you sure that you specified all constant symbols? It is one of my frequent errors.

[Peter230655]

My equation of motion has these free symbols: EOM free symbold: {t, g, l, reibung, m} I specified all, except of course the time t:

state_symbols = tuple((*q_ind, *u_ind))
laenge = len(state_symbols)
print(state_symbols, len(state_symbols))
_constant_symbols = (l, m, g, reibung)_
specified_symbols = (Tx, Ty)

and I gave then values:

par_map = OrderedDict()
par_map[l]       = 2.0
par_map[m]       = 1.0
par_map[g]       = 9.81
par_map[reibung] = 0.

I can send the program. Thanks!

[tjstienstra]

Hmmm, that sounds good.

[Peter230655]

But does not work! :-(

[Peter230655]

Maybe I found the problem: My EOMs contain derivatives, which should not be there, maybe my kinematic equations are wrong. Actually, my OEMs also contain accelerations, so something must be dead wrong with my Kane's equations!

[Peter230655]

I found the problem: I specified the specified_symbols as sm.symbols, and not as me.dynamicsymbols