More docs

Docs/sphinx_documentation/source/FFT.rst

@@ -56,7 +56,9 @@ Below are examples of using :cpp:`FFT:R2C`.
 
 Note that using :cpp:`forwardThenBackward` is expected to be more efficient
 than separate calls to :cpp:`forward` and :cpp:`backward` because some
-parallel communication can be avoided.
+parallel communication can be avoided. It should also be noted that a lot of
+preparation works are done in the construction of an :cpp:`FFT::R2C`
+object. Therefore, one should cache it for reuse if possible.
 
 
 Poisson Solver
@@ -65,4 +67,5 @@ Poisson Solver
 AMReX provides FFT based Poisson solvers. :cpp:`FFT::Poisson` supports all
 periodic boundaries using purely FFT. :cpp:`FFT::PoissonHybrid` is a 3D only
 solver that supports periodic boundaries in the first two dimensions and
-Neumann boundary in the last dimension.
+Neumann boundary in the last dimension. Similar to :cpp:`FFT::R2C`, the
+Poisson solvers should be cached for reuse.

Tests/FFT/Poisson/main.cpp

@@ -14,8 +14,8 @@ int main (int argc, char* argv[])
  BL_PROFILE("main");
 
  AMREX_D_TERM(int n_cell_x = 64;,
- int n_cell_y = 64;,
- int n_cell_z = 64);
+ int n_cell_y = 32;,
+ int n_cell_z = 128);
 
  AMREX_D_TERM(int max_grid_size_x = 32;,
  int max_grid_size_y = 32;,

Tests/FFT/R2C/main.cpp

@@ -13,8 +13,8 @@ int main (int argc, char* argv[])
  {
  BL_PROFILE("main");
 
- AMREX_D_TERM(int n_cell_x = 64;,
- int n_cell_y = 64;,
+ AMREX_D_TERM(int n_cell_x = 128;,
+ int n_cell_y = 32;,
  int n_cell_z = 64);
 
  AMREX_D_TERM(int max_grid_size_x = 32;,