;;;	pursuit_curve.lsp
;;;		Takaya Iwamoto   Nov 24,2002
;;;	Feb 9, 2005 modified input sequence
;;;	Jun 5, 2005 added pursuit_3 case (ellipse)
;;;	Aug 2, 2005 added JPG_YES flag for jpgout option
;;;Test for Pursuit curve
;;;
;;;	Pursuit_linear		The simple case		The target runs along y-axis
;;;	Pursuit_circle					Target moves in a circle
;;;	pursuit_ellipse		Ellipse case		isoclinal trajectories
;;;
(defun c:Pursuit_linear()
	(setup_sysvar)
	(setup_pursuit_1)
	(make_jpg)
	(pursuit_1)
	(setq a_value (car pnt_a))

	(if (= (Yes_or_No "Draw exact curve ?") "_Y")
	
	(draw_pursuit_curve rel_speed a_value))
	(make_jpg)
	(command "_.redraw")
	(make_jpg)
	(reset_sysvar)
);;;PURSUIT_LINEAR
;;;
;(prompt "loading pursuit_11")
;;;
(defun c:Pursuit_11()
	(setup_sysvar)
	(setup_pursuit_1)
	(pursuit_1)
	(setq a_value (car pnt_a))

	(if (= (Yes_or_No "Draw exact curve ?") "_Y")
	
	(draw_pursuit_curve2 x0 y0))
	(reset_sysvar)
);;;PURSUIT_11
;;;
;(prompt "loading pursuit_circle")
;;;
(defun c:Pursuit_circle()
	(setup_sysvar)
	(setup_pursuit_2)
	(make_jpg)
	(pursuit_2)
	(make_jpg)
	(command "_.delay" 1000)
	(command "_.redraw")
	(command "_.layer" "_Off" "layer8" "")
	(make_jpg)
	(reset_sysvar)
);;;PURSUIT_CIRCLE
;;;
;;;PURSUIT_ELLIPSE	Ellipse case   isoclinal trajectories
;;;
(defun C:PURSUIT_ellipse()
	(setup_sysvar)
	(setvar "OSMODE" 512)
	(setup_pursuit_3)
	(make_jpg)
	(pursuit_3)
	(make_jpg)
	(command "_.delay" 1000)
	(command "_.redraw")
	(command "_.layer" "_Off" "layer8" "")
	(make_jpg)
;;recover layer8 for display
	(command "_.layer" "_On" "layer8" "")
	(while (= (Yes_or_No "Want to start from another point on the same ellipse ? ") "_Y")
		(setq ncount 1)
		(entdel red_arrow) (entdel blue_arrow)
		(command "_.point" (setq pnt_c(getpoint "\nGet starting point of the dog(def = 0,1)")))
		(if (= pnt_c nil) (setq pnt_c '(0 1)) )
		
		(setq 	d_ref 1.e10  	d_ab (distance pnt_a pnt_b)  )
	;;;  set arrow at the starting points
		(command "_.insert" "red_arrow" pnt_a 0.5 0.5 -90.)
		(setq red_arrow (entlast))
		(command "_.insert" "blue_arrow" pnt_c 0.5 0.5 (setq theta_0 (rtd (angle pnt_a pnt_c))) )
		(setq blue_arrow (entlast))
		(setq theta_old theta_0)
		
		(pursuit_3)
	)	;;;end of while loop
	(reset_sysvar)
	(setvar "OSMODE" 0)

);;;PURSUIT_ELLIPSE
;;;
;;;SETUP_PURSUIT_1
;;;
(defun setup_pursuit_1()
	(setvar "PDMODE" 32)
	(setq pnt_o '(0 0) pnt_xr '(8 0)
		pnt_1 '(0 -5) pnt_2 '(0 5)
		pnt_y1 '(0 -5.25) pnt_y2 '(0 5) 
		pnt_low '(5 -5) pnt_up '(5 10) pnt_mid '(5 0)
		ncount 0
	)

	(make_line_1 "0" 8 pnt_low pnt_up)
	(make_line_1 "0" 8 pnt_o pnt_xr)
	(make_line_1 "0" 8 pnt_y1 pnt_y2)
	(make_pt "0" 8 pnt_low)
	(make_pt "0" 8 pnt_mid)
	(make_pt "0" 8 pnt_up)
	(make_pt "0" 8 pnt_o)

	(command "_.zoom" "_EXTENT")
	(command "_.regen")
	(command "_.point" (setq pnt_1 (getpoint "\nGet starting point of the rabbit(def = 5,0)")))
		(if (= pnt_1 nil) (setq pnt_1 pnt_mid))
	(command "_.point" (setq pnt_2 (getpoint "\nGet target point of the rabbit(def = 5,10)")))
		(if (= pnt_2 nil) (setq pnt_2 pnt_up))
	(command "_.point" (setq pnt_3 (getpoint "\nGet starting point of the dog(def = 0,0)")))
		(if (= pnt_3 nil) (setq pnt_3 pnt_o))
	(setq rel_speed (getreal "\nRelative speed of the dog(def 2.0) "))
		(if (= rel_speed nil) (setq rel_speed 2.0) )
		
	(setq pnt_a pnt_1
		pnt_b pnt_2
		pnt_c pnt_3
		d_ref 1.e10
	)
	(make_line_1 "0" 8 pnt_3 pnt_1)
	(setq rate (getreal "\nSpecify speed as a distance  % of length AB:(def 0.5)"))
		(if (= rate nil) (setq rate 0.5))
	(setq 	delta (* (distance pnt_a pnt_b) (/ rate 100.)))
	(setq 	speed (getint "\nSpecify speed (1-100) 1:veryfast 100:very slow(def 50)"))
		(if (= speed nil) (setq speed 50))
	
	(setq d_ab (distance pnt_a pnt_b))
	;;;make two arrow blocks
	;set arrow at the starting points
	(command "_.insert" "red_arrow" pnt_a 0.5 0.5 -90.)
		(setq red_arrow (entlast))
	(command "_.insert" "blue_arrow" pnt_c 0.5 0.5 (setq theta_0 (rtd (angle pnt_a pnt_c))) )
		(setq blue_arrow (entlast))
	(setq theta_old theta_0)
);;;
;;;PURSUIT for a straight line case
(defun pursuit_1()
	(setup_sysvar)
	(initget 1 "Yes No yes no y n")
	(setq x (getkword "Ready to go ? (Yes or No)") )
		 
	(while (> d_ref delta)
	;(while (> d_ca delta)
	   	(setq pnt_ab (pld pnt_a pnt_b delta)
			pnt_ca (pld pnt_c pnt_a (* rel_speed delta))
		)
		(slow_line speed "0" 1 pnt_a pnt_ab)
		(slow_line speed "0" 5 pnt_c pnt_ca)
		(setq theta_new (rtd (angle pnt_a pnt_c))
			del_theta (- theta_new theta_old))
	(grdraw pnt_ab pnt_ca 8 )
	(command "_.move" red_arrow "" pnt_a pnt_ab)
		
	(command "_.move" blue_arrow "" pnt_c pnt_ca )
	(command "_.rotate" blue_arrow "" pnt_ca del_theta)
		(setq pnt_a pnt_ab 
			pnt_c pnt_ca
			theta_old theta_new
		)
		(setq d_ab (distance pnt_a pnt_b)
			d_ca (distance pnt_c pnt_a)
			d_ref (min d_ab  d_ca)
		)
	(if (and (= (rem ncount 10) 0) (= JPG_YES 1))
			(command "_.jpgout" (strcat "linear_pursuit_2_" (itoa ncount)) "")
		);;;end of if loop
	(setq ncount (1+ ncount))	;;increment  counter
	);;;end of while loop
	
);;;PURSUIT_1
;;;
;;;CIRCLE_CASE
(defun setup_pursuit_2()
	(setvar "PDMODE" 32)
	(setq pnt_o '(0 0) pnt_xr '(16 0) pnt_xl '(-4 0)
		pnt_y1 '(0 -2.5) pnt_y2 '(0 2.5) ncount 0)
	
	(make_line_1 "0" 8 pnt_xl pnt_xr)
	(make_line_1 "0" 8 pnt_y1 pnt_y2)

	
	(command "_.zoom" "_EXTENT")
	(command "_.regen")
	(setq ref_rad (getreal "\nRadius of the circle (def 2.5)?"))
		(if (= ref_rad nil) (setq ref_rad 2.5))
	(setq	pnt_a (list ref_rad 0))
	
	(make_circle_1 "0" 8 pnt_o ref_rad)
	
	;set arrow at the starting points
	(command "_.insert" "red_arrow" pnt_a 0.5 0.5 -90.)
		(setq red_arrow (entlast))
	;(alert "This is the point where a rabit sits now.")
	;(alert "Pick a point where a dog is now.")
	(command "_.point" (setq pnt_3 (getpoint "\nSet the position of the dog:(def 10,0)")))
		(if (= pnt_3 nil) (setq pnt_3 '(10 0)))
	(setq pnt_c pnt_3)
		(make_pt "0" 1 pnt_a)
		(make_pt "0" 5 pnt_c)
	(command "_.insert" "blue_arrow" pnt_c 0.5 0.5 (setq theta_0 (rtd (angle pnt_a pnt_c))) )
		(setq blue_arrow (entlast))
	
	(command "_.zoom" "_EXTENT")
	(command "_.regen")
		
	(setq 	d_ref 1.e10
		half_pi (* 0.5 pi) two_pi (* 2. pi)
	)
		
	(setq rate (getreal "\nSpecify the speed of the rabbit on the circle path in radian:(def 0.05)"))
		(if (= rate nil) (setq rate 0.05))
	(setq 	 rel_speed (getreal "\nRelative speed of the pursuing dog(def 1.25)"))
		(if (= rel_speed nil) (setq rel_speed 1.25))
	(setq 	speed (getint "\nSpecify speed (1-100) 1:veryfast 100:very slow (def 50)"))
		(if (= speed nil) (setq speed 50))
	(setq 	delta (* rate rel_speed ref_rad)
		 theta_old theta_0 th_old 0. rot_old (- half_pi)
	)
	(make_jpg)
	
	
);;;SETUP_PURSUIT_2
;;;
;;;PURSUIT for a circle case
(defun pursuit_2()
	(initget 1 "Yes No Y N yes no")
	(setq x (getkword "Ready to go ? (Yes or No)") )
	(setq d_ca 1.e10)
	(while (> d_ca (* rate ref_rad))
	   	(setq   th_new (+ th_old rate))
		(if (>= th_new two_pi) (setq th_new (- th_new two_pi)))
		(setq	pnt_ab (list (* ref_rad (cos th_new)) (* ref_rad (sin th_new)) )
			pnt_ca (pld pnt_c pnt_a delta)
		)
		(slow_line speed "0" 1 pnt_a pnt_ab)
		(slow_line speed "0" 5 pnt_c pnt_ca)
		(setq theta_new (rtd (angle pnt_a pnt_c))
			del_theta (- theta_new theta_old)
			del_th (rtd (- th_new th_old))
			)
	;(grdraw pnt_ab pnt_ca 8 )
	(make_line_1 "layer8" 8 pnt_ab pnt_ca)
	(command "_.move" red_arrow "" pnt_a pnt_ab)
	(command "_.rotate" red_arrow "" pnt_ab del_th)
	(command "_.move" blue_arrow "" pnt_c pnt_ca )
	(command "_.rotate" blue_arrow "" pnt_ca del_theta)
		(setq pnt_a pnt_ab 
			pnt_c pnt_ca
			theta_old theta_new
			th_old th_new
		)
		(setq d_ca (distance pnt_c pnt_a))
	(if (and (= (rem ncount 10) 0) (= JPG_YES 1))
			(make_jpg)
		);;;end of if loop
	(setq ncount (1+ ncount))	;;increment  counter
	);;;end of while loop

);;;PURSUIT_2
;;;
;;;	ARROW_BLOCK  (used for defining red_arrow, blue_arrow)
;;;	But once the definition is done, it is not used anymore.
(defun arrow_block()
	(command "_.color" 1)
	(command "_.pline" '(0 0) '(0.433 0.25 ) '(0.433 -0.25 ) '(0 0) '(1 0) "")
	(setq red_pl (entlast))
	(command "_.hatch" "_solid" red_pl "")
	(setq temp_arrow (entlast))
	(command "_.block" "red_arrow" '(0 0) temp_arrow red_pl "")

	(command "_.color" 5)
	(command "_.pline" '(0 0) '(0.433 0.25 ) '(0.433 -0.25 ) '(0 0) '(1 0) "")
	(setq blue_pl (entlast))
	(command "_.hatch" "_solid" blue_pl "")
	(setq temp_arrow (entlast))
	(command "_.bock" "blue_arrow" '(0 0) temp_arrow blue_pl"")
);;;arrow_block
;;
(defun draw_pursuit_curve(k_value a_value)
	(setq x_start 0.0
		x_end a_value
		x_inc 0.001
		a (float a_value)	k (float k_value)
		pow_1 (/ (- k 1.) k)  	pow_2 (/ (+ k 1.) k)
		const1 (/ (expt a  (/ 1. k)) (- 1. k))
		const2 (/ (expt a  (- (/ 1. k))) (+ 1. k) )
		const3 (- (/ (* 2 a) (* (- 1. k) (+ k 1.))))
	)
	(setq pnt_start (list x_start 0.0)
		pnt_end (list x_end 0.0)
	)
		
	(setq del_x (- x_end x_start)
		n_step (/ del_x x_inc)
	)
	(setq step 0)
	(setq pnt_old (list x_start (f_x x_start)))
	(while (<= (setq x_t (+ x_start (* step x_inc))) x_end)
		(setq x_t (+ x_start (* step x_inc))
			y_t  (f_x x_t) 
		)
		(setq pnt_new (list x_t y_t))
		(command "_.line" pnt_old pnt_new "")
		(setq pnt_old pnt_new)
		(setq step (+ 1 step))
	)
);;;DRAW_PURSUIT_CURVE
;(prompt "loading f_x")
;;;
(defun f_x(x_value )
	(setq amx (- a x_value) 
		x1 (* 0.5 k const1 (expt amx pow_1))
		x2 (* 0.5 k const2 (expt amx pow_2))
		x3 (* 0.5 k const3)
		result (+ x1 x2 x3)
	)
);;;F_X
;(prompt "loading curve2")
;;
(defun draw_pursuit_curve2(x0 y0)
	(setq x0 (car pnt_3) y0 (cadr pnt_3) r0 (sqrt (+ (* x0 x0) (* y0 y0)) )
		c1 (+ y0 r0) c2 (- y0 r0) c3 (- (* 3. y0) r0)
		x_start x0
		x_end 0.0
		x_inc 0.001
		
	)
	(setq pnt_start pnt_3
		pnt_end (list x_end 0.0)
	)
		
	(setq del_x (- x_end x_start))
	(setq step 0)
	(setq pnt_old (list x_start (f2_x x_start)))
	(while (>= (setq x_t (- x_start (* step x_inc))) x_end)
		(setq x_t (- x_start (* step x_inc))
			y_t  (f2_x x_t) 
		)
		(setq pnt_new (list x_t y_t))
		(command "_.line" pnt_old pnt_new "")
		(setq pnt_old pnt_new)
		(setq step (+ 1 step))
	)
);;;DRAW_PURSUIT_CURVE
;(prompt "loading f2_x")
;;;
(defun f2_x(x_value )
	(setq eta (* (/ x_value x0) (/ x_value x0) )
		  
		x1 (* 0.25 c1 eta)
		x2 (* 0.25 c2 (log eta))
		x3 (* 0.25 c3 )
		result (+ x1 x2 x3)
	)
);;;F2_X 
;;;SETUP_PURSUIT_3
;;;
(defun setup_pursuit_3()
	(setvar "PDMODE" 32)
	(command "_.viewres" "_Y" 20000)
	(setq pnt_o '(0 0) pnt_xr '(1.6 0) pnt_xl '(-1.6 0)
		pnt_ylow '(0 -1.05) pnt_yup '(0 1.3) ncount 1
	)

	(make_line_1 "0" 8 pnt_xl pnt_xr)
	(make_line_1 "0" 8 pnt_ylow pnt_yup)
	(command "_.zoom" "_EXTENT")
	(command "_.regen")
	
	(setq major_axis (getreal  "\nMajor axis radius ( a ) ="))
		(if (= major_axis nil) (setq major_axis 2.0))
		
	(setq minor_axis (getreal  "\nMinor axis radius ( b ) ="))
		(if (= minor_axis nil) (setq minor_axis 1.0))
		(setq pnt_pa (list major_axis 0) pnt_ma (list (- major_axis) 0)
			pnt_pb (list 0 minor_axis)
		)
	(command "_.ellipse" pnt_ma pnt_pa pnt_pb)
		(setq base_ellipse (entlast))
	(make_pt "0" 0 pnt_pa )
	(make_pt "0" 0 pnt_ma )
	(make_pt "0" 0 pnt_pb )
	(command "_.zoom" "_E")
	
	(setq c_val (sqrt (- (* major_axis major_axis) (* minor_axis minor_axis)) )
		pnt_f1 (list (- c_val) 0) pnt_f2 (list c_val 0)
		def_target '(1 0) 
		def_speed (/ major_axis c_val)
	)
	(make_pt "0" 8 pnt_f1 )	
	(make_pt "0" 8 pnt_f2 )
	(command "_.point" (setq pnt_1 (getpoint "\nGet starting point of the rabbit(def=focus)")))
		(if (= pnt_1 nil) (setq pnt_1 pnt_f1))
	(command "_.point" (setq pnt_2 (getpoint "\nGet target point of the rabbit(def = 0,0)")))
		(if (= pnt_2 nil) (setq pnt_2 '(1 0)) )
	(command "_.point" (setq pnt_3 (getpoint "\nGet starting point of the dog(def = 0,1)")))
		(if (= pnt_3 nil) (setq pnt_3 '(0 1)) )
	(setq rel_speed (getreal "\nRelative speed of the dog(def= a/c) "))
		(if (= rel_speed nil) (setq rel_speed def_speed) )
		
	(setq pnt_a pnt_1
		pnt_b pnt_2
		pnt_c pnt_3
		d_ref 1.e10
	)
	(make_line_1 "0" 8 pnt_a pnt_c)	;;;initial chase direction
	(setq delta (getreal "\nSpecify a unit length of stride for a rabbit(def 0.01)"))
		(if (= delta nil) (setq delta 0.01))
	(setq 	speed (getint "\nSpecify speed (1-100) 1:veryfast 100:very slow(def 50)"))
		(if (= speed nil) (setq speed 50))
	
	(setq d_ab (distance pnt_a pnt_b))
	;set arrow at the starting points
	(command "_.insert" "red_arrow" pnt_a 0.5 0.5 -90.)
		(setq red_arrow (entlast))
	(command "_.insert" "blue_arrow" pnt_c 0.5 0.5 (setq theta_0 (rtd (angle pnt_a pnt_c))) )
		(setq blue_arrow (entlast))
	(setq theta_old theta_0)
;;;jpgout option case
	(make_jpg)
	
);;;
;;;PURSUIT for multiple pursuit case.
(defun pursuit_3(
		; / pnt_as pnt_cs pnt_newa pnt_newc theta_new theta_old
		;d_ab d_ca
		)
	(initget 1 "Yes No yes no y n")
	(setq x (getkword "Ready to go ? (Yes or No)") )
	(setq pnt_as pnt_a pnt_cs pnt_c  delta_0 delta)	 
	(while (> d_ref delta_0)
	   	(setq pnt_newa (pld pnt_as pnt_b delta)
			pnt_newc (pld pnt_cs pnt_as (* rel_speed delta))
		)
		(slow_line speed "0" 1 pnt_as pnt_newa)
		(slow_line speed "0" 5 pnt_cs pnt_newc)
		(setq theta_new (rtd (angle pnt_as pnt_cs))
			del_theta (- theta_new theta_old))
	;(grdraw pnt_newa pnt_newc 8 )
	(make_line_1 "layer8" 8 pnt_newa pnt_newc)
	(command "_.move" red_arrow "" pnt_as pnt_newa)
		
	(command "_.move" blue_arrow "" pnt_cs pnt_newc )
	(command "_.rotate" blue_arrow "" pnt_newc del_theta)
		(setq pnt_as pnt_newa 
			pnt_cs pnt_newc
			theta_old theta_new
		)
		(setq d_ab (distance pnt_as pnt_b)
			d_ca (distance pnt_newc pnt_newa)
			d_ref (min d_ab  d_ca)
		)
		( if (< d_ca 0.5) (setq delta_0 (* 0.5 delta)));;;improves accuracy  ???
	(if  (= (rem ncount 20) 0) (make_pt "0" 0 pnt_newc) )
	(if (and (= (rem ncount 10) 0) (= JPG_YES 1))
			(make_jpg)
		);;;end of if loop
	(setq ncount (1+ ncount))	;;increment  counter
	);;;end of while loop
	(make_pt "0" 0 pnt_as)
	(make_pt "0" 0 pnt_cs)
	
);;;PURSUIT_3
;;;
;;;
;(prompt "loading curve4")
;;
(defun draw_pursuit_curve4(x0 y0)
	(setq x0 (car pnt_3) y0 (cadr pnt_3) r0 (sqrt (+ (* x0 x0) (* y0 y0)) )
		c1 (+ y0 r0) c2 (- y0 r0) c3 (- (* 3. y0) r0)
		x_start x0
		x_end 0.0
		x_inc 0.001
		
	)
	(setq pnt_start pnt_3
		pnt_end (list x_end 0.0)
	)
		
	(setq del_x (- x_end x_start))
	(setq step 0)
	(setq pnt_old (list x_start (f4_x x_start)))
	(while (>= (setq x_t (- x_start (* step x_inc))) x_end)
		(setq x_t (- x_start (* step x_inc))
			y_t  (f4_x x_t) 
		)
		(setq pnt_new (list x_t y_t))
		(command "_.line" pnt_old pnt_new "")
		(setq pnt_old pnt_new)
		(setq step (+ 1 step))
	)
);;;DRAW_PURSUIT_CURVE4
;(prompt "loading f4_x")
;;;
(defun f4_x(x_value )
	(setq  x1 (* C1 (expt (/ x_value a_val) (+ K 1)))
		x2 (* C2 (expt (/ x_value a_val) (- 1 K)))
	
		result (+ x1 x2 Const)
	)
);;;F4_X 
;;;Test case for ellipse
;;;SETUP_PURSUIT_4
;;;
(defun setup_pursuit_4()
	(setvar "PDMODE" 32)
	(command "_.viewres" "_Y" 20000)
	(setq pnt_o '(0 0) pnt_xr '(2 0) pnt_xl '(-2 0)
		pnt_ylow '(0 -2.5) pnt_yup '(0 2.5) 
	)

	(make_line_1 "0" 8 pnt_xl pnt_xr)
	(make_line_1 "0" 8 pnt_ylow pnt_yup)
	(command "_.zoom" "_EXTENT")
	(command "_.regen")
	
	(setq major_axis (getreal  "\nMajor axis radius ( a ) ="))
		(if (= major_axis nil) (setq major_axis 1.0))
		
	(setq minor_axis (getreal  "\nMinor axis radius ( b ) ="))
		(if (= minor_axis nil) (setq minor_axis 2.0))
		(setq pnt_pa (list major_axis 0) pnt_ma (list (- major_axis) 0)
			pnt_pb (list 0 minor_axis)
		)
	(command "_.ellipse" pnt_ma pnt_pa pnt_pb)
		(setq base_ellipse (entlast))
	(make_pt "0" 0 pnt_pa )
	(make_pt "0" 0 pnt_ma )
	(make_pt "0" 0 pnt_pb )

	(setq c_val (sqrt (- (* minor_axis minor_axis) (* major_axis major_axis) ) )
		pnt_f1 (list 0 (- c_val) ) 
		def_target '(1 0) 
		def_speed (/ minor_axis c_val)
		a_val major_axis b_val minor_axis 
		k (/ c_val b_val) alpha (/ (+ b_val c_val) a_val)
		C1 (* 0.5 alpha (/ a_val (+ K 1.)))
		C2 (- (* 0.5 (/ a_val (* alpha (- 1. K))) ))
		Const (- (+ C1 C2))
	)
	(make_pt "0" 0 pnt_f1 )	
		
	;(command "_.point" (setq pnt_1 (getpoint "\nGet starting point of the rabbit(def=focus)")))
	;	(if (= pnt_1 nil) (setq pnt_1 pnt_f1))
	;(command "_.point" (setq pnt_2 (getpoint "\nGet target point of the rabbit(def = 1,0)")))
	;	(if (= pnt_2 nil) (setq pnt_2 '(1 0)) )
	;(command "_.point" (setq pnt_3 (getpoint "\nGet starting point of the dog(def = 0,1)")))
	;	(if (= pnt_3 nil) (setq pnt_3 '(0 1)) )
	;(setq rel_speed (getreal "\nRelative speed of the dog(def= 1.15470) "))
	;	(if (= rel_speed nil) (setq rel_speed def_speed) )
		
	;(setq pnt_a pnt_1
	;	pnt_b pnt_2
	;	pnt_c pnt_3
	;	d_ref 1.e10
	;)
	;(setq delta (getreal "\nSpecify a unit length of stride for a rabbit(def 0.01)"))
	;	(if (= delta nil) (setq delta 0.01))
	;(setq 	speed (getint "\nSpecify speed (1-100) 1:veryfast 100:very slow(def 50)"))
	;	(if (= speed nil) (setq speed 50))
	
	;(setq d_ab (distance pnt_a pnt_b))
	;;set arrow at the starting points
	;(command "_.insert" "red_arrow" pnt_a 0.5 0.5 -90.)
	;	(setq red_arrow (entlast))
	;(command "_.insert" "blue_arrow" pnt_c 0.5 0.5 (setq theta_0 (rtd (angle pnt_a pnt_c))) )
	;	(setq blue_arrow (entlast))
	;(setq theta_old theta_0)
);;;
;;;
;;;COPY_SCALE	copy and then scale the copied entity
;;;
(defun copy_scale(ent_base base_pnt scale_f 
		/ copy_ent )

	(command "_.copy" ent_base "" base_pnt  "")
	(setq copy_ent (entlast))
	(command "_.scale" copy_ent "" base_pnt scale_f )
);;;COPY_SCALE
;;;
;;;Draw scaled ellipses based on the base_ellipse
;;;
(defun scale_ellipse(ent_base)
	(setq pnt_0 '(0 0))
	(while (setq pnt_x (getpoint "\nSelect a point to define half major_axis length"))
		(setq ref_len (abs (car pnt_x))
			base_len (abs (car pnt_ma))
			scale_f (/ ref_len base_len)
		)
		(copy_scale ent_base pnt_0 scale_f)
	);end of while loop
);;;SCALE_ELLIPSE
;;;