fix the left-right/up-down direction in code to make communication correct

examples/heatTransfer/write/Settings.cpp

@@ -64,22 +64,22 @@ Settings::Settings(int argc, char *argv[], int rank, int nproc) : rank{rank}
 
     // determine neighbors
     if (posx == 0)
-        rank_left = -1;
+        rank_up = -1;
     else
-        rank_left = rank - 1;
+        rank_up = rank - 1;
 
     if (posx == npx - 1)
-        rank_right = -1;
+        rank_down = -1;
     else
-        rank_right = rank + 1;
+        rank_down = rank + 1;
 
     if (posy == 0)
-        rank_up = -1;
+        rank_left = -1;
     else
-        rank_up = rank - npx;
+        rank_left = rank - npx;
 
     if (posy == npy - 1)
-        rank_down = -1;
+        rank_right = -1;
     else
-        rank_down = rank + npx;
+        rank_right = rank + npx;
 }