Question #699510 on Yade changed:
https://answers.launchpad.net/yade/+question/699510
Status: Open => Answered
Jan Stránský proposed the following answer:
Hello,
there are two points:
1) NewtonInegrator.gravity. It is not included in O.forces.f
2) i.phys.normalForce and i.phys.shearForce are numbers/vectors SAME for both
interacting bodies, but clearly they must be taken into account oppositely for
each body (Newton's 3rd law of action and reaction)
Below is corrected code. For the second example, replace 0 with 20 (body id)
###
NewtonIntegrator(...,label="integrator")
...
print O.forces.f(0) + newton.gravity * O.bodies[0].state.mass
a=[]
for i in O.bodies[0].intrs():
f = i.phys.normalForce + i.phys.shearForce
if O.bodies[0].id == i.id1: f = -f # HERE
a.append(f)
resultF=Vector3(0,0,0)
for i in range(len(a)):
resultF=resultF+a[i]
resultF += integrator.gravity * O.bodies[0].state.mass # HERE
###
Cheers
Jan
PS: Not important notes:
---
> for i in range(len(a)):
> resultF=resultF+a[i]
a more readable would be:
for f in a:
resultF=resultF+f
or even more "pythonic" without (explicit) loop:
resultF = sum(a, Vector3.Zero)
---
print O.forces.f(20)
a=[]
for i in O.bodies[20].intrs():
20 is repeated code/value, which is generally considered as bad practice (to
change it, you need to be careful to change all occurrences, even more
emphasized with the corrected code).
Better is to use a variable for this:
###
id = 20
print O.forces.f(id)
a=[]
for i in O.bodies[id].intrs():
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