If you have an expression you can use `.replace({q1: q1_sym})`.
The code generation tools in PyDy can be directly used to code gen matrices
with dynamicsymbols:
https://pydy.readthedocs.io/en/stable/codegen/codegen.html
Jason
moorepants.info
+01 530-601-9791
On Mon, Oct 28, 2019 at 6:00 AM Ashith Shyam <[email protected]> wrote:
> Thanks Jason for the reply. As I have mentioned before, my actual system
> is a bit more complex with the manipulator attached to a floating base.
> There are several non-holonomic constraints as well. I am not sure if these
> could be addressed by pydy or may be it will but still I need to go through
> examples and learn and develop again.
> Could you please let me know how to replace the functions of time with
> ordinary symbols. I am expecting something like q1(t) to be q[0] and d
> q1(t) /dt to be dq[0]?
>
> Ash
>
> On Mon, Oct 28, 2019 at 12:39 PM Jason Moore <[email protected]> wrote:
>
>> https://github.com/pydy/pydy will do all this for you with just a few
>> commands.
>>
>> If you want to use the code generation tools in sympy directly, it may
>> help to replace the functions of time with ordinary symbols.
>>
>> Jason
>> moorepants.info
>> +01 530-601-9791
>>
>>
>> On Mon, Oct 28, 2019 at 4:04 AM Ash <[email protected]> wrote:
>>
>>> Hello
>>> I am trying to develop equations of motion using sympy of a complex
>>> system. It takes 4-5 minutes to get the mass matrix (M) and coriolis vector
>>> (C). Hence I decided to use sympy's codegen and try to make it fast.
>>> I can write my equations as
>>>
>>> d^2 *q*/ dt^2 = M_inverse (Tau - C - G)
>>> but M, C, Tau (torque) and G(gravity) are defined with respect to state
>>> variables and its derivatives. And I cant figure out how to do it.
>>>
>>> I am attaching a simple two degree of freedom planar robot's code for
>>> easy understanding of my problem. My state variables are the angles q1(t)
>>> and q2(t) (dynamic symbols). There are other variables like lengths, mass,
>>> inertia of the links which are defined as symbols. M(q(t)), C(q(t), dq(t)),
>>> G(q(t)) matrices are derived symbolically (line 14). My doubt is if I want
>>> to play around with the numerical values of the variables in M, C, and G,
>>> how can I efficiently generate code and cythonize and build wrapper?
>>>
>>> Any help would be really appreciated
>>>
>>> Thanks
>>>
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>
>
> --
> R.B. Ashith Shyam <https://sites.google.com/site/rbashithshyam/>
> +44 7459909812
>
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