update, shorten text in active matter tutorial

doc/tutorials/active_matter/CMakeLists.txt

@@ -1,5 +1,5 @@
 configure_tutorial_target(
   TARGET tutorial_am DEPENDS active_matter.ipynb figures/friction.svg
-  figures/pusher-puller.svg figures/geometry.svg figures/flow_field.svg)
+  figures/pusher-puller.svg figures/geometry.svg)
 
 nb_export(TARGET tutorial_am FILE "active_matter.ipynb" HTML_RUN)

testsuite/scripts/tutorials/test_active_matter.py

@@ -15,6 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import numpy as np
 import unittest as ut
 import importlib_wrapper
 
@@ -23,10 +24,17 @@
     gpu=True,
     ED_N_SAMPLING_STEPS=100000,
     RECT_N_SAMPLES=150,
-    HYDRO_N_STEPS=100
+    HYDRO_N_STEPS=150
 )
 
 
+def curl2d(flow, spacing):
+    # curl_z = d(v_y) / dx - d(v_x) / dy
+    dvy_dx = np.gradient(flow[:, :, 1], spacing[0], axis=0)
+    dvx_dy = np.gradient(flow[:, :, 0], spacing[1], axis=1)
+    return dvy_dx - dvx_dy
+
+
 @skipIfMissingFeatures
 class TestActMat(ut.TestCase):
     system = tutorial.system
@@ -52,6 +60,20 @@ def test_hydrodynamics(self):
             tutorial.system.analysis.linear_momentum(
                 include_particles=False)[2], 0)
 
+    def test_flow_profile(self):
+        """
+        Check the flow field curl is symmetric with 4 local extrema
+        centered around the particle.
+        """
+        flow_field = tutorial.vels[:, :, (0, 2)]
+        curl = curl2d(flow_field, 2 * [tutorial.lbf.agrid])
+        curl_percent = curl * 100. / np.max(np.abs(curl))
+        threshold_percent = 85.
+        self.assertGreaterEqual(curl_percent[16, 20], threshold_percent)
+        self.assertGreaterEqual(curl_percent[18, 16], threshold_percent)
+        self.assertLessEqual(curl_percent[16, 16], -threshold_percent)
+        self.assertLessEqual(curl_percent[18, 20], -threshold_percent)
+
 
 if __name__ == "__main__":
     ut.main()