Thanks a lot! It turned out that init_vprinting() gives the behavior I
wanted.
In case others want to go down this path, I am appending a minimal notebook
entry which shows the syntax. I am really impressed that diff(L, xdot)
just works, and that I can use solve to get algebraic expressions for
velocities and accelerations.
One additional question - is there a better way to get the time variable
than dynamicsymbols._t ? I look at that leading underscore as an
indication that I shouldn't be touching it from user code.
------------------
In [1]:
from sympy.physics.vector import dynamicsymbols
from sympy import diff, symbols, S
from sympy.physics.vector import init_vprinting
init_vprinting()
# Simplest test case .. particle of mass m in uniform gravitational field g
x = dynamicsymbols('x')
t = dynamicsymbols._t
xdot = diff(x,t)
m, g = symbols('m g')
T = (m * xdot**2)/S(2) #kinetic energy
V = m*g*x # potential energy is just mgh
L = T - V
#Euler-Lagrange equation
diff(L, xdot,t) - diff(L,x)
Out[1]:
gm+mx¨
On Wednesday, August 13, 2014 10:24:47 PM UTC-7, Jason Moore wrote:
>
> Oh, you should use
>
> sympy.physics.vector.init_printing()
>
> If you want the dot notation in latex in your notebooks.
>
>
> Jason
> moorepants.info
> +01 530-601-9791
>
>
> On Wed, Aug 13, 2014 at 10:23 PM, Jason Moore <[email protected]
> <javascript:>> wrote:
>
>> You can subclass a printer and have it do what you want. You can see here:
>>
>>
>> https://github.com/sympy/sympy/blob/master/sympy/physics/vector/printing.py#L145
>>
>> where we subclass the latex printer and get the \dot{} notation for
>> derivatives, for example. There is also an example here:
>>
>> http://docs.sympy.org/dev/modules/printing.html
>>
>> of subclassing to do custom derivative printing. Maybe exactly what you
>> want.
>>
>> The LagrangesMethod in sympy.physics.mechanics works with the classes
>> available in that package (RigidBody, ReferemceFrame, etc). The other one
>> is more basic math. So if you want to write all the math yourself then
>> maybe the later is preferable, but if you want to use the objects in
>> sympy.physics.mechanics to build up a rigid body system and find the
>> equations of motion, the use the former.
>>
>>
>> Jason
>> moorepants.info
>> +01 530-601-9791
>>
>>
>> On Wed, Aug 13, 2014 at 10:13 PM, Rathmann <[email protected]
>> <javascript:>> wrote:
>>
>>> Hello,
>>>
>>> I have been watching the lectures of Susskind's "Theoretical Minimum"
>>> course, and using Sympy with IPython notebook to take notes, and work
>>> through some of the examples.
>>>
>>> Sympy is serious overkill for this purpose, but overall it has been
>>> working well.
>>>
>>> A couple of questions:
>>>
>>> - What is the best way to deal with dynamics variables and the dot
>>> convention for printing? (In physics, the first time derivative of x is
>>> often written as \dot{x} instead of dx/dt.) Is there an easy way to
>>> get IPython notebook to print dynamics variables using the dot
>>> convention,
>>> and still give the nice LaTeX-rendered equations? If I use vprint (from
>>> physics.vector), I get the variables with primes, but just a text
>>> rendering of the equations.
>>> - I notice sympy.physics.mechanics.LagrangesMethod and
>>> sympy.calculus.euler.euler_equations both implement Lagrangian
>>> mechanics.
>>> Is one of these more "official" than the other? Both seem to work for
>>> the
>>> very simple examples I have tried.
>>>
>>> Thanks
>>>
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>>
>
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