diff --git a/Parameters_May21.md b/Parameters_May21.md
index c8598eb..e16f1f5 100644
--- a/Parameters_May21.md
+++ b/Parameters_May21.md
@@ -2639,11 +2639,86 @@ void evolve_wave(phi, psi, xy_in)
 
 ### 4 May 21 - Why the Bunimovich stadium is chaotic ###
 
-**Program:** `xxx.c`
+**Program:** `particle_billiard.c` (adapted to August 1 version)
 
-**Initial condition in function `animation()`:** `xxx`
+**Initial condition in function `animation()`:** `init_line_config(0.0, -0.05, 0.0, 0.05, 0.0, configs);`
 
 ```
+#define MOVIE 0         /* set to 1 to generate movie */
+
+#define WINWIDTH 	1280  /* window width */
+#define WINHEIGHT 	720   /* window height */
+
+#define XMIN -2.0
+#define XMAX 2.0	/* x interval */
+#define YMIN -1.125
+#define YMAX 1.125	/* y interval for 9/16 aspect ratio */
+
+#define SCALING_FACTOR 1.0       /* scaling factor of drawing, needed for flower billiards, otherwise set to 1.0 */
+
+/* Choice of the billiard table, see global_particles.c */
+
+#define B_DOMAIN 2      /* choice of domain shape */
+
+#define CIRCLE_PATTERN 2    /* pattern of circles */
+
+#define NMAXCIRCLES 1000        /* total number of circles (must be at least NCX*NCY for square grid) */
+#define NCX 15            /* number of circles in x direction */
+#define NCY 20            /* number of circles in y direction */
+
+#define LAMBDA 0.5	/* parameter controlling shape of domain */
+#define MU 0.035          /* second parameter controlling shape of billiard */
+#define FOCI 1          /* set to 1 to draw focal points of ellipse */
+#define NPOLY 9             /* number of sides of polygon */
+#define APOLY -1.0           /* angle by which to turn polygon, in units of Pi/2 */ 
+#define DRAW_BILLIARD 1     /* set to 1 to draw billiard */
+#define DRAW_CONSTRUCTION_LINES 0   /* set to 1 to draw additional construction lines for billiard */
+#define PERIODIC_BC 0       /* set to 1 to enforce periodic boundary conditions when drawing particles */
+
+#define RESAMPLE 0      /* set to 1 if particles should be added when dispersion too large */
+#define DEBUG 0         /* draw trajectories, for debugging purposes */
+
+/* Simulation parameters */
+
+#define NPART 5000       /* number of particles */
+#define NPARTMAX 100000	/* maximal number of particles after resampling */
+#define LMAX 0.01       /* minimal segment length triggering resampling */ 
+#define DMIN 0.02       /* minimal distance to boundary for triggering resampling */ 
+#define CYCLE 1         /* set to 1 for closed curve (start in all directions) */
+
+#define NSTEPS 3000     /* number of frames of movie */
+#define TIME 750       /* time between movie frames, for fluidity of real-time simulation */ 
+#define DPHI 0.00002    /* integration step */
+#define NVID 150         /* number of iterations between images displayed on screen */
+
+/* Decreasing TIME accelerates the animation and the movie                               */
+/* For constant speed of movie, TIME*DPHI should be kept constant                        */
+/* However, increasing DPHI too much deterioriates quality of simulation                 */
+/* NVID tells how often a picture is drawn in the animation, increase it for faster anim */
+/* For a good quality movie, take for instance TIME = 400, DPHI = 0.00005, NVID = 100    */
+
+/* Colors and other graphical parameters */
+
+#define NCOLORS 10      /* number of colors */
+#define COLORSHIFT 0     /* hue of initial color */ 
+#define RAINBOW_COLOR 0  /* set to 1 to use different colors for all particles */
+#define FLOWER_COLOR 0   /* set to 1 to adapt initial colors to flower billiard (tracks vs core) */
+#define NSEG 100         /* number of segments of boundary */
+#define LENGTH 0.05      /* length of velocity vectors */
+#define BILLIARD_WIDTH 3    /* width of billiard */
+#define PARTICLE_WIDTH 2    /* width of particles */
+#define FRONT_WIDTH 3       /* width of wave front */
+
+#define BLACK 1             /* set to 1 for black background */
+#define COLOR_OUTSIDE 0     /* set to 1 for colored outside */ 
+#define OUTER_COLOR 270.0   /* color outside billiard */
+#define PAINT_INT 0         /* set to 1 to paint interior in other color (for polygon/Reuleaux) */
+
+
+#define PAUSE 1000       /* number of frames after which to pause */
+#define PSLEEP 1         /* sleep time during pause */
+#define SLEEP1  1        /* initial sleeping time */
+#define SLEEP2  1000      /* final sleeping time */
 
 ```