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• parsing
  • Added an example output verification test for the autolev parser. (#15165 by @NikhilPappu and @moorepants)

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Based on #15006.
#### Brief description of what is fixed or changed
This is an example test that ensures the sympy code generated from the autolev parser generates the same output as the autolev code.
@NikhilPappu This is what I'm imagining for output verification tests. Let me know what you think. We should implement some of these for the more complicated examples you have (at least). I'd really like to see this kind of test for all the examples (in addition or instead of the current text comparison tests).
#### Other comments
Note that the position vector test doesn't pass. I think the parser outputs an incorrect result.
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* parsing
  * Added an example output verification test for the autolev parser.
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Update

The release notes on the wiki have been updated.

@moorepants Did you have a look at the output comparisons of the examples in the GitLab repo?

Here is the code the parser produced:

import sympy.physics.mechanics as me
import sympy as sm
import math as m
import numpy as np
frame_c=me.ReferenceFrame('c')
frame_d=me.ReferenceFrame('d')
frame_f=me.ReferenceFrame('f')
fd, dc = me.dynamicsymbols('fd dc')
fdd, dcd = me.dynamicsymbols('fd dc', 1)
fdd2, dcd2 = me.dynamicsymbols('fd dc', 2)
r, l=sm.symbols('r l', real=True)
point_o=me.Point('o')
point_e=me.Point('e')
frame_d.orient(frame_f, 'Axis', [fd, frame_f.x])
frame_c.orient(frame_d, 'Axis', [dc, frame_d.y])
point_e.set_pos(point_o, r*frame_d.y-l*frame_c.x)
point_e.set_pos(point_o, (point_e.pos_from(point_o)).express(frame_d))
point_e.set_vel(frame_f, ((point_e.pos_from(point_o)).dt(frame_f)).express(frame_d))
point_e.set_acc(frame_f, ((point_e.vel(frame_f)).dt(frame_f)).express(frame_d))

I think the correct code should be:

# Note that Autolev users could name variables "sm" and "me", so these could get clobbered.
import sympy as sm
import sympy.physics.mechanics as me
# Don't import math (ever!) and don't import numpy if not needed.
frame_c = me.ReferenceFrame('c')
frame_d = me.ReferenceFrame('d')
frame_f = me.ReferenceFrame('f')
fd, dc = me.dynamicsymbols('fd, dc')
# Use _d for dot and _dd for double dot, etc.
fd_d, dc_d = me.dynamicsymbols('fd, dc', 1)
fd_dd, dc_dd = me.dynamicsymbols('fd, dc', 2)
r, l = sm.symbols('r l', real=True)
point_o = me.Point('o')
point_e = me.Point('e')
# Need to check whether the correct DCMs are generated. Is this F wrt to D or D wrt F? I always forget.
frame_d.orient(frame_f, 'Axis', (fd, frame_f.x))
frame_c.orient(frame_d, 'Axis', (dc, frame_d.y))
point_o.set_pos(point_e, r*frame_d.y - l*frame_c.x)
point_o.set_pos(point_e, point_o.pos_from(point_e).express(frame_d))
point_e.set_vel(frame_f, point_e.pos_from(point_o).dt(frame_f).express(frame_d))
point_e.set_acc(frame_f, point_e.vel(frame_f).df(frame_f).express(frame_d))

@moorepants Did you have a look at the output comparisons of the examples in the GitLab repo?

No, I don't recall being told about them.

@moorepants I had added output comparisons to some of the examples in the GitLab repo. They aren't very detailed though. In many cases, I have just shown the equivalence (I have only included comments in the example files) of the final eoms.
Here is one of them (from the chaos_pendulum example):

# Output Comparison Results
# =========================
# -> (51) ZERO[1] = 0
# -> (52) ZERO[2] = 0
# -> (53) ZERO[3] = -G*LB*MB*SIN(THETA) - G*MA*LA*SIN(THETA) - 2*(IBXX-IBYY)*SIN(PHI)*COS(PHI)*ALPHA*OMEGA - (MB*LB^2+IAYY+IBYY+MA*LA^2+(IBXX-IBYY)*SIN(PHI)^2)*OMEGA'
# -> (54) ZERO[4] = (IBXX-IBYY)*SIN(PHI)*COS(PHI)*OMEGA^2 - IBZZ*ALPHA'
subs_dict = {g:9.81,lb:0.2,w:0.2,h:0.1,ma:0.01,mb:0.1,theta:np.deg2rad(90),phi:np.deg2rad(0.5),omega:1,alpha:2,omegad:3,alphad:4}
zero_autolev = sm.Matrix([[0],[0]])
zero_autolev[0] = (-g*lb*mb*sm.sin(theta) - g*ma*la*sm.sin(theta) - 2*(ibxx-ibyy)*sm.sin(phi)*sm.cos(phi)*alpha*omega -\
(mb*lb**2+iayy+ibyy+ma*la**2+(ibxx-ibyy)*sm.sin(phi)**2)*omegad).subs(subs_dict).evalf()
zero_autolev[1] = ((ibxx-ibyy)*sm.sin(phi)*sm.cos(phi)*omega**2-ibzz*alphad).subs(subs_dict).evalf()
print(zero_autolev)
# Matrix([[-0.217020788909953], [-0.00133624206773955]])
zero[0] = zero[0].subs(subs_dict).evalf()
zero[1] = zero[1].subs(subs_dict).evalf()
print(zero)
# Matrix([[-0.217020788909953], [-0.00133624206773955]])
# which shows that zero_autolev and zero are the same equations.

I am not able to find output examples in the Gitlab repo. Can you point me specifically to one (or them)?

@moorepants I had just put the comparisons (mainly comments) at the end of the example files.

I see. Ideally we encode them as I've done in this PR, as also ideally have as much as we can in the SymPy repo. Note that on my first one I seemingly uncovered an error(s) in the parser output.

@moorepants
These tests certainly look better. The main reason I have included them in the GitLab repo is that the outputs were related to the examples (most of which are from Autolev texts). I think we could keep them there and make GitLab-CI run those tests by using SymPy.
As for the error, I shall fix it soon as the fix is easy.

Note that the P_O_E> parsed output is still incorrect.

@moorepants Now that I took another look at the position vectors, I think the parser does it the right way.
p_o_e> is the position vector of e wrt o. The change I made was different and I have now reversed that.

>>> import sympy.physics.mechanics as me
>>> import sympy as sm
>>> import math as m
>>> import numpy as np
>>> n = me.ReferenceFrame('n')
>>> o = me.Point('p')
>>> e = me.Point('o')
>>> l = sm.symbols('l')
# p_o_e> = l*n.x
>>> e.set_pos(o, l*n.x)
>> e.pos_from(o)
l*n.x

You are correct. I forgot the syntax. Here is a snippet from Online Dynamics that confirms:

The position vector goes from the second character to the third character.

Sorry to lead you astray.

In the doctest builds I'm getting:

$ bin/test_travis.sh
+[[ true == \t\r\u\e ]]
+python bin/test_setup.py
Traceback (most recent call last):
  File "bin/test_setup.py", line 27, in <module>
    assert setup.tests == test_list, set(setup.tests).symmetric_difference(set(test_list))
AssertionError: {'sympy.parsing.autolev.tests'}

Not quite sure what that is.

@moorepants I placed the current test file test_autolev.py in parsing/tests and put the comparison files in parsing/autolev/test_examples so there is no directory called parsing/autolev/tests.
So parsing/autolev/tests needs to be added in the modules = [ and tests = [ lists of setup.py.

This is ready for final review and merge.

@NikhilPappu Would you mind reviewing this?

@moorepants It looks great to me!

@ayushmankoul

self.output_code.append("import sympy.physics.mechanics as me\n")
self.output_code.append("import sympy as sm\n")
self.output_code.append("import math as m\n")
self.output_code.append("import numpy as np\n")

These should also have _me, _sm_ and _np. Make this change, do the test_autolev.py thing to update the tests and you should be good to go for the most part.

@NikhilPappu I updated this thing in code but I am not able to run skipped tests on my local machine.The following code in test_autolev.py is causing assertion errors due to failure of test examples:

Whereas on altering the above code as following yields no assertion error on local machine:

Sorry for messing things up again and again.

It'd be best to move this discussion to the respective issue or PR.