Fix #165 Use Corrected CFL Criteria

A. Taflove & M. E. Brodwin
IEEE Trans. on Microwave Theory and Techniques, August 1975
Formula (7)

src/picongpu/include/simulation_defines/unitless/gridConfig.unitless

@@ -35,15 +35,20 @@ namespace picongpu
     CONST_VECTOR(float_X,simDim,cellSize,CELL_WIDTH,CELL_HEIGHT,CELL_DEPTH);
 
 #if (SIMDIM==DIM3)
-    const float_X CELL_VOLUME = CELL_WIDTH * CELL_HEIGHT *CELL_DEPTH;
-    /* Courant-Friedrichs-Levy-Condition for Field Solver: */
-    PMACC_CASSERT_MSG(Courant_Friedrichs_Levy_condition_failure____check_your_gridConfig_param_file,  
-                     (PMACC_MIN(CELL_DEPTH,PMACC_MIN(CELL_WIDTH,CELL_HEIGHT))/SPEED_OF_LIGHT/DELTA_T)>1.77f); 
+    const float_X CELL_VOLUME = CELL_WIDTH * CELL_HEIGHT * CELL_DEPTH;
+    const float_X INV_CELL2_SUM = 1.0 / ( CELL_WIDTH  * CELL_WIDTH  )
+                                + 1.0 / ( CELL_HEIGHT * CELL_HEIGHT )
+                                + 1.0 / ( CELL_DEPTH  * CELL_DEPTH  );
 #elif(SIMDIM==DIM2)
-    const float_X CELL_VOLUME = CELL_WIDTH * CELL_HEIGHT ;
-        /* Courant-Friedrichs-Levy-Condition for Field Solver: */
-    PMACC_CASSERT_MSG(Courant_Friedrichs_Levy_condition_failure____check_your_gridConfig_param_file,
-                      (PMACC_MIN(CELL_WIDTH,CELL_HEIGHT)/SPEED_OF_LIGHT/DELTA_T)>1.77f);               
+    const float_X CELL_VOLUME = CELL_WIDTH * CELL_HEIGHT;
+    const float_X INV_CELL2_SUM = 1.0 / ( CELL_WIDTH  * CELL_WIDTH  )
+                                + 1.0 / ( CELL_HEIGHT * CELL_HEIGHT );
+#else
+    const float_X INV_CELL2_SUM = 1.0 / ( CELL_WIDTH  * CELL_WIDTH  );
 #endif
+
+    /* Courant-Friedrichs-Levy-Condition for Yee Field Solver: */
+    PMACC_CASSERT_MSG(Courant_Friedrichs_Levy_condition_failure____check_your_gridConfig_param_file,
+                     (SPEED_OF_LIGHT*SPEED_OF_LIGHT*DELTA_T*DELTA_T*INV_CELL2_SUM)<=1.0);
 
 }