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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