basic questions on law-test.py

Hi Giulia, let me try to answer. I should say at start that it is possible that we will find some bugs in LawTester, as it was written only recently.

1. Local coordinate system; the 0th component is normal (between sphere's centers), 1st and 2nd components are 2 shear directions, perpendicular to the normal. Local system definition depends on IGeom class that is in use. If you use ScGeom (which only knows normal, i.e. local x axis), the other two axes will be chosen arbitrarily at first, then tracked following motion of both particles.

2. That is correct; if there is no rolling, then shear can be created in geometrically different ways, although the resulting shear will be the same -- imagine (i) one sphere fixed, the other one rotating around an axis going through its center and perpendicular to the interaction [that is rotWeight==1] (ii) one sphere fixed, the other one translated around the other one on circular arc centered at the first sphere's center (distance does not change), without underoging any rotation [that is rotWeight==0].

You can assign other values to rotWeight as well (including those ouside the 0...1 range) and the result should still be the same.

Note that rotWeight is ignored when mutual rotations (bending/twisting) are considered by the IGeom, since then, shear must be applied in such a way that it does not create bending and vice versa (that takes away that degree of freedom expressed by rotWeight).

3. Oh yes, they should be the same... I will have a look tomorrow, hope that is fine for you.

If you use ScGeom6D: I will have to add support for it to LawTester (I have not done it yet, and I did not expect someone will use it that soon); OTOH it is not complicated and I will have a look tomorrow morning probably.

Also I did some changes in LawTester today to make it more intuitive (hopefully); your old code will work, and some warnings will tell you how to change it then.

re 3.: Don't you have displIsRel==True? (https://www.yade-dem.org/sphinx/yade.wrapper.html#yade.wrapper.LawTester.displIsRel) That might explain it.

Hi Giulia, I added proper docs for LawTester, I hope they answer your questions now. I am planning to add some images as well, but that has to be postponed now. Cheers!

https://www.yade-dem.org/sphinx/yade.wrapper.html#yade.wrapper.LawTester

Thank you, that is very helpful!

But now I think there are some issues with qt.view, since when I run the script I get the displacements plotted, but I don't see the balls moving in the 3d view (I could see it using the 2598 release).

Sorry, Giu, I fixed that in the last commit (2612), it was a bit of previous changes that broke it.

Now (2612) it perfectly works.

Thank you
Giulia

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