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[Mukesh Tiwari <question201064@xxxxxxxxxxxxxxxxxxxxx>]

New question #201064 on Yade:
https://answers.launchpad.net/yade/+question/201064

Hi 
I am trying to look at how Yade updates postion and velocity through a simple example of a body falling freely under gravity. The code is:

O.bodies.append([utils.sphere((0,0,1),.5)])

b = O.bodies[0]
#b.state.vel=(0,0,0) 
print O.time,b.state.vel[2],b.state.pos[2]


O.engines=[
   ForceResetter(),
   NewtonIntegrator(damping=0,gravity=(0,0,-9.81)),
   PyRunner(command='addData()',iterPeriod=1),
]

O.dt = 0.1
		

def addData():
    print O.time,b.state.vel[2],b.state.pos[2]

O.run(10,True)

Now the output which I obtain is :

0.0    0.0     1.0
0.1  -1.962  0.7057
0.2  -2.943  0.4114
0.3  -3.924  0.019
0.4  -4.905  -0.4715
0.5  -5.886  -1.0601
0.6  -6.867  -1.7468
0.7  -7.848  -2.5316
0.8  -8.829  -3.4145
0.9  -9.81   -4.3955

The velocity at dt =0.1  should be -0.981 but it gives the expected value at 2*dt. Similarly the position at dt=0.1 is what one expects at 6*dt. I am not sure if there is something wrong in what I do or if there is some other issue.

Thanks
Mukesh

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