%@DATE: 31 mai 2005 input fichierps; InitFichierPS(-150,-150,150,150); u = 1.2cm; % La longueur de la tige. l = 4; % La position du point décrivant l'ellipse sur la tige. f := 0.7; vardef Point(expr p) = draw p withpen pencircle scaled 4; draw p withpen pencircle scaled 3 withcolor white; enddef; % L'ellipse; path e; for i=0 upto 200: beginfig(i+1); pair A,B,E; if i<=50: A = (i*l/50,0) scaled u; elseif i<=150: A = (2l-i*l/50,0) scaled u; else: A = (i*l/50-4l,0) scaled u; fi; x := (xpart A)/u; k := l*sqrt(1-(x/l)*(x/l)); B := (0,k) scaled u; if (i>50) and (i<150): B := B yscaled -1; fi; E = f[B,A]; drawoptions(withcolor 0.6white); draw ((-1.1l,0)--(1.1l,0)) scaled u; draw ((0,1.1l)--(0,-1.1l)) scaled u; drawoptions(); drawarrow (0,0)--(A scaled 0.95) withpen pencircle scaled 1.25; if i=0: e := E; else: e := e -- E; draw e withpen pencircle scaled 1 withcolor blue; fi drawoptions(withpen pensquare scaled 2 withcolor (1,0.08,0.58)); draw A--B; drawoptions(); Point(A); Point(B); Point(E); endfig; endfor; end