I found my mistake, matter closed.
Am Mo., 7. März 2022 um 13:22 Uhr schrieb Peter Stahlecker <
peter.stahlec...@gmail.com>:
> I tried on a 'small' example, and N_y.suns({sm.Derivative(q1, t): u1})
> worked just fine !!
> No idea, what is going on.
>
> Am So., 6. März 2022 um 15:18 Uhr schrieb Peter Stahlecker <
> peter.stahlec...@gmail.com>:
>
>> I am playing around with an ellipse, which rotates in 3D.
>> In its own coordinate system A, its equation of course is
>>
>> x**2/a**2 + y**2/b**2 + z**2/c**2 = 1
>>
>> A rotates relative to N, the generalized coordinates are q1, q2, q3,
>> dq1/dt = u1, etc.
>> I express the rotated ellipse in N, by using A.variable_map(N), now the
>> coordinates are, say, N_x, N_y, N_z.
>> Using sympy.solve I solve the ellipse equation for N_y, I get two
>> solutions, of which I take the one I need, so, say, I get
>> N_y = f(N_x, N_z, q1, d2, d3, a, b, c,…)
>> I want the speed of N_y, so I write:
>>
>> Speed_N_y = f(…..).diff(t)
>>
>> Now my problem starts:
>> In Speed_N_y, there are terms like Derivative(q1(t), t), and same for
>> q2, q3.
>> Of course, these terms are u1, u2, u3, but I cannot find a way to replace
>> Derivative(q1(t), t) with u1, etc.
>> I tried Speed_N_y.subs({Derivative(q1(t), t): u2}) but this did not
>> work.
>> I tried Speed_N_y.subs({q1.diff(t): u1}) also this did not work.
>> I also tried to get rid of these Derivative terms by writing
>> NY_lam = lambdify( …, Speed_N_y, {‚Derivative(q1(t), t)‘: u1})
>> This did not give an error - but also did not accomplish anything.
>>
>> Of course, when I try to lambdify my Speed_N_y and then try to evaluate
>> it numerically the problems come up, as this Derivative(q1(t), t) is
>> unknown.
>>
>> Any help is GREATLY appreciated! Thanks!
>>
>>
>>
>>
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