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Prototype System class. #81

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merged 18 commits into from
Aug 7, 2014
Merged

Prototype System class. #81

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77cd5d4
Prototype System class.
chrisdembia Jul 29, 2014
61cd1a7
WIP: Started tests for System class.
moorepants Jul 29, 2014
29fc9cb
Removing default behaviors from System class.
chrisdembia Jul 30, 2014
418c1fc
Fix bug with mass spring damper kwarg.
chrisdembia Jul 30, 2014
2a5b721
WIP Write most of the System class, with tests.
chrisdembia Jul 30, 2014
3c6344a
Changed the arguments to the generated rhs to support dictionaries.
moorepants Aug 1, 2014
bfe2138
Added test for specified dict.
moorepants Aug 1, 2014
9aef7d8
Updated all code to use new dictionary inputs for generate_ode_function.
moorepants Aug 1, 2014
8f30674
About to redo System defaults.
chrisdembia Aug 3, 2014
35cba4d
Replace calls to find_ with custom methods.
chrisdembia Aug 3, 2014
d0d945f
Fix some minor typos.
chrisdembia Aug 3, 2014
0ca1d2b
Not making constants, specifieds, and initial conditions properties.
chrisdembia Aug 3, 2014
331aa33
Finish System class, with passing tests.
chrisdembia Aug 4, 2014
826f4d5
Update double_pendulum example to use System.
chrisdembia Aug 4, 2014
964dbe7
Update documentation for System class.
chrisdembia Aug 4, 2014
1778fee
Minor cleanup.
moorepants Aug 5, 2014
fd981e7
Restore the fast way of parsing specifieds.
chrisdembia Aug 7, 2014
f6c03a3
Edits to the README.
moorepants Aug 7, 2014
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16 changes: 8 additions & 8 deletions examples/double_pendulum/double_pendulum.py
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Expand Up @@ -33,11 +33,11 @@
KM = KanesMethod(N, q_ind=[q1, q2], u_ind=[u1, u2], kd_eqs=kd)


(fr, frstar) = KM.kanes_equations(FL, BL)
kdd = KM.kindiffdict()
mass_matrix = KM.mass_matrix_full
forcing_vector = KM.forcing_full
qudots = mass_matrix.inv() * forcing_vector
qudots = qudots.subs(kdd)
qudots.simplify()

KM.kanes_equations(FL, BL)
#kdd = KM.kindiffdict()
#mass_matrix = KM.mass_matrix_full
#forcing_vector = KM.forcing_full
#qudots = mass_matrix.inv() * forcing_vector
#qudots = qudots.subs(kdd)
#qudots.simplify()
#
41 changes: 7 additions & 34 deletions examples/double_pendulum/simulate.py
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Expand Up @@ -9,44 +9,17 @@

from double_pendulum import *

# List the symbolic arguments
# ===========================

# Constants
# ---------

constants = {l: 10.0, m: 10.0, g: 9.81}

# Time-varying
# ------------

coordinates = [q1, q2]

speeds = [u1, u2]


# Generate function that returns state derivatives
# ================================================

xdot_function = generate_ode_function(mass_matrix, forcing_vector,
constants.keys(), coordinates, speeds)
initial_conditions = {q1: 1.0, q2: 0.0, u1: 0.0, u2: 0.0}


# Specify numerical quantities
# ============================

initial_coordinates = [1.0, 0.0]
initial_speeds = [0.0, 0.0]
x0 = concatenate((initial_coordinates, initial_speeds), axis=1)

args = {'constants': constants.values()}


# Simulate
# ========
sys = System(KM, constants=constants,
initial_conditions=initial_conditions)

frames_per_sec = 60
final_time = 5.0

t = linspace(0.0, final_time, final_time * frames_per_sec)
x = odeint(xdot_function, x0, t, args=(args,))
times = linspace(0.0, final_time, final_time * frames_per_sec)

x = sys.integrate(times)
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This is what I had been implying for re-integrating Scene visualization stuff.
So that we supply times and sys to the Scene class, and is easier to handle than the existing structure.
I am ready to work on integrating this code with Scene class(after tomorrow).

But also there will be some backwards incompatible changes(in Scene class as well), when this is integrated into Scene.

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Yes, that is why we are creating this, so that you can have something easier to work with in your viz code. It won't be ready tomorrow, but please help contribute to this so we can get it done more quickly.


5 changes: 2 additions & 3 deletions examples/double_pendulum/visualize.py
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Expand Up @@ -51,14 +51,13 @@
# this, we create a world frame that is rotated +90 degrees about the N frame's
# z direction.
world_frame = N.orientnew('world', 'Axis', [0.5 * pi, N.z])
scene = Scene(world_frame, O,
scene = Scene(sys, world_frame, O,
linkP_viz_frame, linkR_viz_frame, sphereP_viz_frame, sphereR_viz_frame)
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Is there any way, that we can use System to eliminate the ReferenceFrame and Point argument supplied here.
Maybe they can be saved in System class too?

so that all we need to do is:

scene = Scene(sys, vframes_as_a_list_or_tuple)

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That would be nice to clean up the Scene constructor. However, I am not sure this is a good idea. Those two arguments are specific to how the visualization looks, and they have been useful for me before. We can consider this again down the line when System becomes bigger and potentially manages the viz info. But for now (this PR), System does not handle viz info.

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I think you have to have the option of providing any frame or point as the base viz frame. You could snatch the base frame from the Methods as a default frame, and maybe you could go through all the points stored in the Methods class and find one that has zero velocity in the base frame as a default.



# Create the visualization
# ========================

scene.generate_visualization_json(coordinates + speeds, constants.keys(), x,
constants.values())
scene.generate_visualization_json(times)

scene.display()
18 changes: 15 additions & 3 deletions pydy/codegen/tests/models.py
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Expand Up @@ -9,7 +9,8 @@
import sympy.physics.mechanics as me


def generate_mass_spring_damper_equations_of_motion(external_force=True):
def generate_mass_spring_damper_equations_of_motion(external_force=True,
only_return_kane=False):
"""Returns the symbolic equations of motion and associated variables for a
simple one degree of freedom mass, spring, damper system with gravity
and an optional external specified force.
Expand All @@ -26,8 +27,16 @@ def generate_mass_spring_damper_equations_of_motion(external_force=True):
| F
V

Parameters
----------
only_return_kane : bool, optional (default: False)
If True, this method only returns the KanesMethod object.

Returns
-------
kane : KanesMethod
If the keyword argument `only_return_kane` is True, this is the only
object returned.
mass_matrix : sympy.MutableMatrix, shape(2,2)
The symbolic mass matrix of the system which are linear in
derivatives of the states.
Expand Down Expand Up @@ -90,8 +99,11 @@ def generate_mass_spring_damper_equations_of_motion(external_force=True):
else:
specified = None

return (mass_matrix, forcing_vector, constants, coordinates, speeds,
specified)
if only_return_kane:
return kane
else:
return (mass_matrix, forcing_vector, constants, coordinates, speeds,
specified)


def generate_n_link_pendulum_on_cart_equations_of_motion(n, cart_force=True,
Expand Down
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