RZ PSATD, make blocking_factor a power of 2 (#2572)

* With RZ PSATD, make blocking_factor a power of 2

* Fix typo

Co-authored-by: Edoardo Zoni <59625522+EZoni@users.noreply.github.com>

Co-authored-by: Edoardo Zoni <59625522+EZoni@users.noreply.github.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/Source/Utils/WarpXUtil.cpp b/Source/Utils/WarpXUtil.cpp
index d77a35b3a..277385d49 100644
--- a/Source/Utils/WarpXUtil.cpp
+++ b/Source/Utils/WarpXUtil.cpp
@@ -555,9 +555,15 @@ void CheckGriddingForRZSpectral ()
     Vector<int> blocking_factor_x(max_level+1);
     Vector<int> max_grid_size_x(max_level+1);
 
-    // Set the radial block size to be equal to the radial grid size.
-    blocking_factor_x[0] = n_cell[0];
-    max_grid_size_x[0] = n_cell[0];
+    // Set the radial block size to be the power of 2 greater than or equal to
+    // the number of grid cells. The blocking_factor must be a power of 2
+    // and the max_grid_size should be a multiple of the blocking_factor.
+    int k = 1;
+    while (k < n_cell[0]) {
+        k *= 2;
+    }
+    blocking_factor_x[0] = k;
+    max_grid_size_x[0] = k;
 
     for (int lev=1 ; lev <= max_level ; lev++) {
         // For this to be correct, this needs to read in any user specified refinement ratios.