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[Xiaohu Tao <question672525@xxxxxxxxxxxxxxxxxxxxx>]

Question #672525 on Yade changed:
https://answers.launchpad.net/yade/+question/672525

    Status: Answered => Open

Xiaohu Tao is still having a problem:
Hi, Jérôme

Thank you so much for the detailed explanation.

I read the background of  yade. Can I understand in this way? "U" is the
position, U(0) is the position at Iter 0, U(1) is the position at Iter
1, and U(2) is the position at Iter 2. "V" is the mean velocity and "a"
is the acceleration. in my code a=gravity. △t=1, U(0)=(0,0,0)

So

V(1)=V(0)+a*△t  while "V(0)=0", V(1)=(0,0,-9.81)*1=(0,0,-9.81), this is
just the mean  velocity, NOT  the instantaneous velocity at time 0+△t

U(1)=U(0)+V(1)*△t=(0,0,0)+(0,0,-9.81)*1=(0,0,-9.81)

V(2)=V(1)+a*△t =(0,0,-9.81)+(0,0,-9.81)*1=(0,0,-19.62)

U(2)=U(1)+V(2)*△t=(0,0,-9.81)+(0,0,-19.62)=(0,0,-29.43)

------------------------------------------------------------------------------------------------------------------------

In my understanding：(1) the value of  V(0)=0 is the key of  the error,
so the error is formed in the first iter. (2) the velocity showed by
yade is the  mean velocity in one iter.


Xiaohu

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