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[Chareyre <question172107@xxxxxxxxxxxxxxxxxxxxx>]

Question #172107 on Yade changed:
https://answers.launchpad.net/yade/+question/172107

Chareyre proposed the following answer:
@Viet, there is no relation with the number of particles. The equations
are exact be it with 1 particle (example below).

I finally checked on my side... I don't know how you crunch the numbers
guys, but you surely compute something the wrong way.

Here are my numbers with 1 particle (I got to decrease the time-step,
else the stress control is a bit lost with only 1 sphere...):

step 0: porosity= 0.720940373948968
step 40: porosity=0.594615817413609, e11=0.125334930132997, e22=0.155608210807015, e33=0.0924666030771256

ln(de/(1+e0)) gives -0.37340974
vs.
e11+e22+e33 gives 0.373409744

Hurray! 
No matter overlaps, number of particles, or large strains. Strain values are exact, modulo computer precision.

Try to do your calculations with my numbers and let's see if we find the
same results.

Note that the strain values given by the triaxial engines are true
strains (sorry if it was not clear in my previous post), you don't have
to compute the log on your side. It also means that we are not obliged
to reset strain after isotropic compaction: since the strain is always
exact we can simply substract strains from the different stages to
define strains in one given stage.

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