From d89b6a997e2ea04d40e69e2d700fdb2d12492a45 Mon Sep 17 00:00:00 2001
From: richb2k <75949649+richb2k@users.noreply.github.com>
Date: Sat, 2 Nov 2024 08:38:20 -0400
Subject: [PATCH] ElmerGrid, add calculate mesh pieces function.  Translated
 from Fortran to plain C.  Add helpful notice if a non-conforming mesh is
 detected.

---
 elmergrid/src/egextra.c | 110 ++++++++++++++++++++++++++++++++++++++++
 elmergrid/src/egextra.h |   1 +
 elmergrid/src/fempre.c  |   3 ++
 3 files changed, 114 insertions(+)

diff --git a/elmergrid/src/egextra.c b/elmergrid/src/egextra.c
index 7a39f671ae..318de492b4 100644
--- a/elmergrid/src/egextra.c
+++ b/elmergrid/src/egextra.c
@@ -820,7 +820,117 @@ int SaveSizeInfo(struct FemType *data,struct BoundaryType *bound,
   return(0);
 }
 
+int MeshPieces(struct FemType *data,int nomesh,int nomeshes,int info)
+{
+  int i,j,k,n;
+  int MinIndex,MaxIndex,NoPieces,NoCorners,Loop,Ready;
+  int *MeshPiece=NULL,*PiecePerm=NULL;
+  // Indexes only needs to hold the max number of dofs per element
+  int Indexes[100];
+
+  if(nomeshes > 1) {
+    printf("Calculate Mesh Pieces in mesh[%d] of [%d] meshes:\n",nomesh,nomeshes);
+  } else {
+    printf("Calculate Mesh Pieces in mesh:\n");
+  }
+
+  n = data->noknots;
+  MeshPiece = calloc(n+1, sizeof(int) );
+  if(MeshPiece == NULL) {
+    printf("Allocating space for MeshPiece[] failed.\n");
+    return(1);
+  }
+
+  /*  Only set the piece for the nodes that are used by some element
+      For others the marker will remain zero. */
+  for(i=1; i<=data->noelements; i++) {
+    NoCorners = data->elementtypes[i]%100;
+    for(j=0; j<NoCorners; j++) {
+      MeshPiece[data->topology[i][j]] = 1;
+    }
+  }
+
+  j = 0;
+  for(i=1; i<=n; i++) {
+    if(MeshPiece[i] > 0) {
+      j++;
+      MeshPiece[i] = j;
+    }
+  }
+  if( n > j) {
+    printf("Number of non-body (hanging) nodes in mesh is %d\n", n-j );
+    printf("Consider running ElmerGrid with -autoclean command\n");
+  }
+
+  /* We go through the elements and set all the piece indexes to minimum index
+     until the mesh is unchanged. Thereafter the whole piece will have the minimum index
+     of the piece.  */
+  Ready = 0;
+  Loop = 0;
+
+  while(!Ready) {
+    Ready = 1;
+    for(i=1; i<=data->noelements; i++) {
+      MaxIndex = 0;
+      MinIndex = n;
+
+      NoCorners = data->elementtypes[i]%100;
+      for(j=0; j<NoCorners; j++) {
+        Indexes[j] = data->topology[i][j];
+      }
+      for(j=0; j<NoCorners; j++) {
+        for(k=0; k<NoCorners; k++) {
+          if(MaxIndex <  MeshPiece[Indexes[k]] )
+            MaxIndex = MeshPiece[Indexes[k]];
+          if(MinIndex >= MeshPiece[Indexes[k]] )
+            MinIndex = MeshPiece[Indexes[k]];
+        }
+        if(MaxIndex > MinIndex) {
+          MeshPiece[Indexes[j]] = MinIndex;
+          Ready = 0;
+        }
+      }
+    }
+    Loop++;
+  }
+/*  printf("Mesh coloring loops: %d\n",Loop); */
 
+/*
+  MaxIndex = 0;
+  for(i=1; i<=n; i++)
+    if(MeshPiece[i] > MaxIndex) MaxIndex = MeshPiece[i];
+*/
+
+  /*  Compute the true number of different pieces  */
+  if(MaxIndex == 1) {
+    NoPieces = 1;
+  } else {
+    NoPieces = 0;
+    PiecePerm = calloc(MaxIndex+1, sizeof(int) );
+    if(PiecePerm == NULL) {
+      printf("Allocating space for PiecePerm[] failed.\n");
+      return(1);
+    }
+    for(i=1; i<=n; i++) {
+      j = MeshPiece[i];
+      if( j == 0) continue;
+      if(PiecePerm[j] == 0) {
+        NoPieces++;
+        PiecePerm[j] = NoPieces;
+      }
+    }
+    free(PiecePerm);
+  }
+  if(NoPieces == 1) {
+    printf("There is a single piece in the mesh, so the mesh is conforming.\n");
+  } else {
+    printf("Number of separate pieces in mesh is %d\n", NoPieces);
+    printf("The mesh is non-conforming.  If not expecting a non-conforming\n");
+    printf("mesh, then refer to the Elmer User Forum for help.\n");
+  }
+  free(MeshPiece);
+  return(0);
+}
 
 int SaveElmerInputFemBem(struct FemType *data,struct BoundaryType *bound,
 			 char *prefix,int decimals,int info)
diff --git a/elmergrid/src/egextra.h b/elmergrid/src/egextra.h
index aac36de55d..4219ebe3b8 100644
--- a/elmergrid/src/egextra.h
+++ b/elmergrid/src/egextra.h
@@ -26,6 +26,7 @@ int SaveSizeInfo(struct FemType *data,struct BoundaryType *bound,
 		 char *prefix,int info);
 int SaveElmerInputFemBem(struct FemType *data,struct BoundaryType *bound,
 			 char *prefix,int decimals, int info);
+int MeshPieces(struct FemType *data,int nomesh,int nomeshes,int info);
 
 void InspectVector(Real *vector,int first,int last,Real *min,
 		   Real *max,int *mini,int *maxi);
diff --git a/elmergrid/src/fempre.c b/elmergrid/src/fempre.c
index c8290c4b12..0f7c3c4aca 100644
--- a/elmergrid/src/fempre.c
+++ b/elmergrid/src/fempre.c
@@ -784,6 +784,9 @@ int main(int argc, char *argv[])
   if(info) for(k=0;k<nomeshes;k++)
     BoundingBox(&data[k],k,nomeshes,info);
 
+  if(info) for(k=0;k<nomeshes;k++)
+    MeshPieces(&data[k],k,nomeshes,info);
+
   if(eg.nosave) {
     Goodbye();
     return(0);