For the people developing and maintaining the mechanics modules, you may
want to look at the following book which treats mechanics problems with
some new methods. Describing rotations is greatly simplified -
https://link.springer.com/book/10.1007/0-306-47122-1
On 2/14/22 12:40 PM, Peter Stahlecker wrote:
Dear Jason,
As to the speed of the new terms, I simply tried it, using the
equations of motion of a one body pendulum.
There is no difference to the older terms:
with the /body/ version the the rhs has 863, 824 operations.
with the axis version, 2 intermediate frames, the rhs has 43,722
operations.
The operations count was /exactly/ the same with older and newer terms.
Take care, Peter
On Mon 14. Feb 2022 at 18:04 Peter Stahlecker
<[email protected]> wrote:
Dear Jason,
Just read you latest addition about vectors and reference frames.
Small question:
In order to rotate a frame relative to another one, you use these
terms
/A.orient_axis(N, ..)/
/A.orient_body_fixed(N, …)/
I assume, these are the new versions for
A.orientnew(N, ‚Axis‘, …)
A.orientnew(N, ‚Body, …)
You might recall, that I ‚empirically‘ found that the /Body/
version created much larger equations of motion compared to using
‚intermediate ‚/Axis/‘ versions.
Is it better to use /orient_body_fixed,/ to avoid this issue of
larger equations of motion?
Thanks & take care!
Peter
On Sun 6. Feb 2022 at 08:19 Peter Stahlecker
<[email protected]> wrote:
Dear Jason,
Thanks a lot for your explanation! Clear!
I checked on metaclasses, but I must admit I mostly
understood, that a simple user like me should not mess with
them! :-))
Peter
On Sun 6. Feb 2022 at 07:49 Jason Moore <[email protected]>
wrote:
Peter,
All `dynamicsymbols` is, is:
f = Function('f')
t = symbols('t')
f_of_t = f(t)
The last line `f(t)` is generating a new class of type f,
instead of using a predefined class (look up metaclasses).
So the user, typically not aware of this element in
Python, is confused about what they are working with in
the last line. It is just the way SymPy Function works.
There are open issues about trying to change it to
something more sensible for the user to understand.
Jason
moorepants.info <http://moorepants.info>
+01 530-601-9791
On Sun, Feb 6, 2022 at 7:39 AM Peter Stahlecker
<[email protected]> wrote:
My question is more for my ‚general education‘ in sympy.
I write this little program
/from sympy.physics.mechanics import */
/import sympy as sm/
/a = dynamicsymbols(‚a‘)/
/b = sm.symbols(‚b‘)/
/
/
/print(‚type of a:‘, type(a))/
/print(‚type of b:‘, type(b))/
I get this result:
/type of a: a/
/type of b: class sympy.core.symbols.Symbols/
Is seems that *a* does not have a type. How can that
be? I thought in python ‚everything‘ has a type.
Thanks!
Any explanation is highly appreciated!
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Best regards,
Peter Stahlecker
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Best regards,
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Best regards,
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