use maximum rather than minimum decimation factor for DFT convergence…

… criteria (#1796)

* use maximum rather than minimum decimation factor for DFT convergence criteria

* Update src/dft.cpp

Co-authored-by: Steven G. Johnson <stevenj@mit.edu>

Co-authored-by: Steven G. Johnson <stevenj@mit.edu>

python/simulation.py

@@ -4527,7 +4527,7 @@ def stop_when_dft_decayed(tol=1e-11, minimum_run_time=0, maximum_run_time=None):
     closure = {'previous_fields':0, 't0':0, 'dt':0, 'maxchange':0}
     def _stop(_sim):
         if _sim.fields.t == 0:
-            closure['dt'] = max(1/_sim.fields.dft_maxfreq()/_sim.fields.dt,_sim.fields.min_decimation())
+            closure['dt'] = max(1/_sim.fields.dft_maxfreq()/_sim.fields.dt,_sim.fields.max_decimation())
         if maximum_run_time and _sim.round_time() > maximum_run_time:
             return True
         elif _sim.fields.t <= closure['dt'] + closure['t0']:

src/dft.cpp

@@ -316,21 +316,21 @@ double dft_chunk::norm2() const {
   return sum;
 }
 
-// return the minimum decimation factor across
+// return the maximum decimation factor across
 // all dft regions
-int fields::min_decimation() const {
-  int mindec = std::numeric_limits<int>::max();
+int fields::max_decimation() const {
+  int maxdec = 1;
   for (int i = 0; i < num_chunks; i++)
     if (chunks[i]->is_mine())
-      mindec = std::min(mindec, chunks[i]->min_decimation());
-  return min_to_all(mindec);
+      maxdec = std::max(maxdec, chunks[i]->max_decimation());
+  return max_to_all(maxdec);
 }
 
-int fields_chunk::min_decimation() const {
-  int mindec = std::numeric_limits<int>::max();
+int fields_chunk::max_decimation() const {
+  int maxdec = std::numeric_limits<int>::min();
   for (dft_chunk *cur = dft_chunks; cur; cur = cur->next_in_chunk)
-    mindec = std::min(mindec, cur->get_decimation_factor());
-  return mindec;
+    maxdec = std::max(maxdec, cur->get_decimation_factor());
+  return maxdec;
 }
 
 // return the maximum abs(freq) over all DFT chunks

src/meep.hpp

@@ -1572,7 +1572,7 @@ class fields_chunk {
   void update_dfts(double timeE, double timeH, int current_step);
   double dft_norm2() const;
   double dft_maxfreq() const;
-  int min_decimation() const;
+  int max_decimation() const;
 
   void changing_structure();
 };
@@ -2000,7 +2000,7 @@ class fields {
   void update_dfts();
   double dft_norm();
   double dft_maxfreq() const;
-  int min_decimation() const;
+  int max_decimation() const;
 
   dft_flux add_dft_flux(const volume_list *where, const double *freq, size_t Nfreq,
                         bool use_symmetry = true, bool centered_grid = true,