From 58f82fccbde862da486a444f9ed6dfc2af6d7bf3 Mon Sep 17 00:00:00 2001
From: Henry Weller <http://cfd.direct>
Date: Mon, 4 Sep 2023 11:57:27 +0100
Subject: [PATCH] functionObjects::volFieldValue: Filter processors without
 zone cells for max/min

Resolves bug-report https://bugs.openfoam.org/view.php?id=4014
---
 .../fieldValues/volFieldValue/volFieldValue.C |  8 +++---
 .../fieldValues/volFieldValue/volFieldValue.H |  1 +
 .../volFieldValue/volFieldValueTemplates.C    | 28 +++++++++++++------
 3 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.C b/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.C
index 1a53e1859c..cfb66e2cef 100644
--- a/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.C
+++ b/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.C
@@ -194,22 +194,22 @@ bool Foam::functionObjects::fieldValues::volFieldValue::processValues
     {
         case operationType::min:
         {
-            compareScalars(values, result, lessOp<scalar>());
+            compareScalars(values, vGreat, result, lessOp<scalar>());
             return true;
         }
         case operationType::minMag:
         {
-            compareScalars(mag(values), result, lessOp<scalar>());
+            compareScalars(mag(values), vGreat, result, lessOp<scalar>());
             return true;
         }
         case operationType::max:
         {
-            compareScalars(values, result, greaterOp<scalar>());
+            compareScalars(values, -vGreat, result, greaterOp<scalar>());
             return true;
         }
         case operationType::maxMag:
         {
-            compareScalars(mag(values), result, greaterOp<scalar>());
+            compareScalars(mag(values), -vGreat, result, greaterOp<scalar>());
             return true;
         }
         default:
diff --git a/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.H b/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.H
index 011c8ffeb4..b5fb235ccb 100644
--- a/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.H
+++ b/src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.H
@@ -193,6 +193,7 @@ protected:
         void compareScalars
         (
             const scalarField& values,
+            const scalar emptyVal,
             Result<scalar>& result,
             const Op& op
         ) const;
diff --git a/src/functionObjects/field/fieldValues/volFieldValue/volFieldValueTemplates.C b/src/functionObjects/field/fieldValues/volFieldValue/volFieldValueTemplates.C
index 02d32c6fc8..23a5145213 100644
--- a/src/functionObjects/field/fieldValues/volFieldValue/volFieldValueTemplates.C
+++ b/src/functionObjects/field/fieldValues/volFieldValue/volFieldValueTemplates.C
@@ -79,23 +79,33 @@ template<class Op>
 void Foam::functionObjects::fieldValues::volFieldValue::compareScalars
 (
     const scalarField& values,
+    const scalar emptyVal,
     Result<scalar>& result,
     const Op& op
 ) const
 {
-    label i = 0;
-    forAll(values, j)
+    // Check if the zone on this processor is non-zero sized
+    if (values.size())
     {
-        if (op(values[j], values[i]))
+        label i = 0;
+        forAll(values, j)
         {
-            i = j;
+            if (op(values[j], values[i]))
+            {
+                i = j;
+            }
         }
+
+        result.value = values[i];
+        result.celli = celli(i);
+        result.cc = fieldValue::mesh_.C()[result.celli];
+    }
+    else
+    {
+        result.value = emptyVal;
     }
 
-    result.value = values[i];
-    result.celli = celli(i);
     result.proci = Pstream::parRun() ? Pstream::myProcNo() : -1;
-    result.cc = fieldValue::mesh_.C()[result.celli];
 
     reduce
     (
@@ -147,12 +157,12 @@ bool Foam::functionObjects::fieldValues::volFieldValue::processValues
     {
         case operationType::minMag:
         {
-            compareScalars(mag(values), result, lessOp<scalar>());
+            compareScalars(mag(values), vGreat, result, lessOp<scalar>());
             return true;
         }
         case operationType::maxMag:
         {
-            compareScalars(mag(values), result, greaterOp<scalar>());
+            compareScalars(mag(values), -vGreat, result, greaterOp<scalar>());
             return true;
         }
         default: