Test LB profile observables in parallel (#4583)

Fixes #4582, fixes #4581, fixes #4584

Description of changes:
- check that LB profile observables work in parallel
- remove outdated warning in the user guide that mentioned they could not run in parallel
- fix regression in the LB sedimentation tutorial

doc/tutorials/lattice_boltzmann/lattice_boltzmann_sedimentation.ipynb

@@ -77,6 +77,8 @@
     "import espressomd.observables\n",
     "import espressomd.accumulators\n",
     "\n",
+    "espressomd.assert_features([\"LENNARD_JONES\", \"LB_BOUNDARIES\"])\n",
+    "\n",
     "# imports for data handling, plotting, and progress bar\n",
     "import numpy as np\n",
     "import matplotlib.pyplot as plt\n",

src/python/espressomd/observables.py

@@ -267,10 +267,6 @@ class LBVelocityProfile(ProfileObservable):
     ``sampling_*``. Note that a small delta leads to a large number of sample
     points and carries a performance cost.
 
-    .. WARNING::
-        In case of the CPU version of the LB fluid implementation, this observable
-        currently only works for a single core.
-
     Parameters
     ----------
     n_x_bins : :obj:`int`

testsuite/python/CMakeLists.txt

@@ -238,7 +238,7 @@ python_test(FILE polymer_linear.py MAX_NUM_PROC 4)
 python_test(FILE polymer_diamond.py MAX_NUM_PROC 4)
 python_test(FILE auto_exclusions.py MAX_NUM_PROC 1)
 python_test(FILE observable_cylindrical.py MAX_NUM_PROC 4)
-python_test(FILE observable_cylindricalLB.py MAX_NUM_PROC 1 LABELS gpu)
+python_test(FILE observable_cylindricalLB.py MAX_NUM_PROC 2 LABELS gpu)
 python_test(FILE analyze_chains.py MAX_NUM_PROC 1)
 python_test(FILE analyze_distance.py MAX_NUM_PROC 1)
 python_test(FILE analyze_acf.py MAX_NUM_PROC 1)
@@ -247,7 +247,7 @@ python_test(FILE rescale.py MAX_NUM_PROC 2)
 python_test(FILE array_properties.py MAX_NUM_PROC 4)
 python_test(FILE analyze_distribution.py MAX_NUM_PROC 1)
 python_test(FILE observable_profile.py MAX_NUM_PROC 4)
-python_test(FILE observable_profileLB.py MAX_NUM_PROC 1 LABELS gpu)
+python_test(FILE observable_profileLB.py MAX_NUM_PROC 2 LABELS gpu)
 python_test(FILE rotate_system.py MAX_NUM_PROC 4)
 python_test(FILE es_math.py MAX_NUM_PROC 1)
 python_test(FILE random_pairs.py MAX_NUM_PROC 4)

testsuite/python/observable_cylindricalLB.py

@@ -33,7 +33,7 @@ class CylindricalLBObservableCommon:
     Testcase for the CylindricalLBObservables.
 
     """
-    system = espressomd.System(box_l=3 * [15])
+    system = espressomd.System(box_l=3 * [14])
     system.time_step = 0.01
     system.cell_system.skin = 0.4
 

testsuite/python/observable_profileLB.py

@@ -34,9 +34,9 @@
 
 TIME_STEP = 0.1
 AGRID = 0.7
-BOX_L_X = 17.0 * AGRID
-BOX_L_Y = 15.0 * AGRID
-BOX_L_Z = 13.0 * AGRID
+BOX_L_X = 16.0 * AGRID
+BOX_L_Y = 14.0 * AGRID
+BOX_L_Z = 12.0 * AGRID
 VISC = .7
 DENS = 1.7
 LB_PARAMS = {'agrid': AGRID,
@@ -78,9 +78,9 @@ def tearDown(self):
 
     def set_fluid_velocities(self):
         """Set an x dependent fluid velocity."""
-        for x in range(int(self.system.box_l[0] / AGRID)):
-            for y in range(int(self.system.box_l[1] / AGRID)):
-                for z in range(int(self.system.box_l[2] / AGRID)):
+        for x in range(int(np.around(self.system.box_l[0] / AGRID))):
+            for y in range(int(np.around(self.system.box_l[1] / AGRID))):
+                for z in range(int(np.around(self.system.box_l[2] / AGRID))):
                     self.lbf[x, y, z].velocity = [float(x), 0.0, 0.0]
 
     def test_velocity_profile(self):
@@ -98,7 +98,7 @@ def test_velocity_profile(self):
             for y in range(obs_data.shape[1]):
                 for z in range(obs_data.shape[2]):
                     self.assertAlmostEqual(
-                        obs_data[x, y, z, 0], float(x), places=5)
+                        obs_data[x, y, z, 0], float(x), delta=2e-5)
         self.assertEqual(np.prod(obs_data.shape),
                          LB_VELOCITY_PROFILE_PARAMS['n_x_bins'] *
                          LB_VELOCITY_PROFILE_PARAMS['n_y_bins'] *