; use two sliders, to change the mean and standard deviation of
; a normal distribution whose density is graphed
 
(def mean 0)
(def sd 1)
(def pl (plot-points '(-10 10) '(0 .4) :title "Normal Density"))
(send pl :clear-points)
(defun sqr(x) (* x x))
(defun ndens (x)
        (* (exp (* (sqr (/ (- x mean) sd)) -.5)) (/ 1 (* (sqrt (* 2 pi)) sd)))
)
(defun doplot ()
        (send pl :clear-lines :draw nil)
        (def llim (- mean (* sd 4)))
        (def ulim (+ mean (* sd 4)))
        (def xval (rseq llim ulim 100))
;  the mapcar function applies the named function (ndens) to each element
;  in the xval list
        (send pl :add-lines xval (mapcar #'ndens xval))
)
 
; produce the initial plot, with mean 0 and sd 1
(doplot)
 
(defun change-mean(m)
        (def mean m)
        (doplot)
)
(defun change-sd(s)
        (def sd (cond ((= s 0) sd) (t s)))
        (doplot)
)
 
(def i1 (interval-slider-dialog (list -5 5) :points 40 :action 'change-mean
        :title "Mean" ))
(send i1 :value 0)
(def i2 (interval-slider-dialog (list .2 5) :points 19 :action 'change-sd
        :title "SD" ))
(send i2 :value 1)