Find max value in parallel safely

src/festim/exports/maximum_surface.py

@@ -1,3 +1,5 @@
+from mpi4py import MPI
+
 import numpy as np
 
 import festim.exports.surface_quantity as sq
@@ -28,5 +30,8 @@ def compute(self):
         indices = self.surface.locate_boundary_facet_indices(
             solution.function_space.mesh
         )
-        self.value = np.max(self.field.solution.x.array[indices])
+
+        self.value = solution.function_space.mesh.comm.allreduce(
+            np.max(self.field.solution.x.array[indices]), op=MPI.MAX
+        )
         self.data.append(self.value)

src/festim/exports/maximum_volume.py

@@ -1,3 +1,5 @@
+from mpi4py import MPI
+
 import numpy as np
 
 from festim.exports import VolumeQuantity
@@ -27,5 +29,8 @@ def compute(self):
         """
         solution = self.field.solution
         indices = self.volume.locate_subdomain_entities(solution.function_space.mesh)
-        self.value = np.max(self.field.solution.x.array[indices])
+
+        self.value = solution.function_space.mesh.comm.allreduce(
+            np.max(self.field.solution.x.array[indices]), op=MPI.MAX
+        )
         self.data.append(self.value)

src/festim/exports/minimum_surface.py

@@ -1,3 +1,5 @@
+from mpi4py import MPI
+
 import numpy as np
 
 import festim.exports.surface_quantity as sq
@@ -28,5 +30,8 @@ def compute(self):
         indices = self.surface.locate_boundary_facet_indices(
             solution.function_space.mesh
         )
-        self.value = np.min(self.field.solution.x.array[indices])
+
+        self.value = solution.function_space.mesh.comm.allreduce(
+            np.min(self.field.solution.x.array[indices]), op=MPI.MIN
+        )
         self.data.append(self.value)

src/festim/exports/minimum_volume.py

@@ -1,3 +1,5 @@
+from mpi4py import MPI
+
 import numpy as np
 
 from festim.exports import VolumeQuantity
@@ -26,7 +28,8 @@ def compute(self):
         """
         solution = self.field.solution
         indices = self.volume.locate_subdomain_entities(solution.function_space.mesh)
-        # FIXME: np.min/np.max is not parallel safe (unique value per process)
-        # Needs to use a reduction operation (MPI.comm.allreduce(..., op=...))
-        self.value = np.min(self.field.solution.x.array[indices])
+
+        self.value = solution.function_space.mesh.comm.allreduce(
+            np.min(self.field.solution.x.array[indices]), op=MPI.MIN
+        )
         self.data.append(self.value)