Oops - except the m \ddot{x} formats properly in the notebook. On Thursday, August 14, 2014 11:09:08 AM UTC-7, Rathmann wrote: > > 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 <moore...@gmail.com> 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 <rathm...@gmail.com> 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 >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "sympy" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to sympy+un...@googlegroups.com. >>>> To post to this group, send email to sy...@googlegroups.com. >>>> Visit this group at http://groups.google.com/group/sympy. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/sympy/fe1737e3-3b19-40e5-8983-5d64bfad8e2f%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/sympy/fe1737e3-3b19-40e5-8983-5d64bfad8e2f%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> >>
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