```New question #655697 on Yade:
```
Hello,
The following code is an example from Yade. I know the first part is about
hydrostatic compression. But how to understand "stressMask=0b000111" here? (
goal=(-1e7,-1e7,-1e7, 0,0,0)  ) As we know, 0 means strain controlled and 1
means stress controlled, I think stressMask may be set as 0b111111. Could you
please give me some suggestions? Thanks.

# peri3dController_triaxialCompression.py
# script, that explains funcionality and input parameters of Peri3dController
on the example of
# triaxial compression.
#   Firstly, a hydrostatic preassure is applied, then a strain along z axis is
increasing
# while x- and y- stress is constant
#   The simulation is run on rotated cell to enable localization and strain
softening
# (you can also try simulation with command sp.toSimulation() with no rotation,
# in this case there is almost no difference, but in script
peri3dController_shear,
# the cell rotation has significant effect)

from yade import pack,plot,qt

# define material
O.materials.append(FrictMat())

# create periodic assembly of particles
initSize=1.2
angle=0
rot=Matrix3(cos(angle),0,-sin(angle), 0,1,0, sin(angle),0,cos(angle))
sp.toSimulation(rot=rot)

# plotting
plot.live=False
plot.plots={'iter':('sx','sy','sz','syz','szx','sxy',),'iter_':('ex','ey','ez','eyz','ezx','exy',),'ez':('sz',)}
iter=O.iter,iter_=O.iter,
sx=p3d.stress[0],sy=p3d.stress[1],sz=p3d.stress[2],
syz=p3d.stress[3],szx=p3d.stress[4],sxy=p3d.stress[5],
ex=p3d.strain[0],ey=p3d.strain[1],ez=p3d.strain[2],
eyz=p3d.strain[3],ezx=p3d.strain[4],exy=p3d.strain[5],
)

O.dt=PWaveTimeStep()/2

# define the first part of simulation, hydrostatic compression
O.engines=[
ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb()]),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom()],

[Ip2_FrictMat_FrictMat_FrictPhys()],[Law2_ScGeom_FrictPhys_CundallStrack()]),
NewtonIntegrator(),
Peri3dController(       goal=(-1e7,-1e7,-1e7, 0,0,0), # Vector6 of
prescribed final values
nSteps=500,
reached."; O.pause()',
youngEstimation=.5e9, # needed, when
only nonzero prescribed values are stress
maxStrain=.5,
label='p3d'
),
]
O.run(); O.wait()

# second part, z-axis straining and constant transversal stress
O.engines=[
ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb()]),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom()],

[Ip2_FrictMat_FrictMat_FrictPhys()],[Law2_ScGeom_FrictPhys_CundallStrack()]),
NewtonIntegrator(),
Peri3dController(       goal=(-1e7,-1e7,-4e-1, 0,0,0), # Vector6 of
prescribed final values
nSteps=1000,
xxPath=[(0,1),(1,1)], # the first (time) zero defines
the initial value of stress considered nonzero
yyPath=[(0,1),(1,1)],
doneHook='print "Simulation with Peri3dController
finished."; O.pause()',
maxStrain=.5,
label='p3d',
strain=p3d.strain, # continue from value reached in
previous part
stressIdeal=Vector6(-1e7,-1e7,0, 0,0,0), # continue
from value reached in previous part
),
]
O.run();O.wait()
plot.plot(subPlots=False)

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