package require BLT
namespace import ::blt::*

proc compute args {
puts $::a
puts $::b
puts $::c
puts $::d
#puts [vector expr {($::a * (::x ^ 3))  + ($::b * (::x ^ 2)) + ($::c * ::x) +  $::d}]
puts [vector expr {::x}]

}

label .l -text "Function: ax^3 + bx^2 + cx + d"        ; table . .l 0,0

graph .g -width 700 -height 600 -bd 2 -relief groove   ; table . .g 1,0 -fill both
Blt_ZoomStack .g

vector ::x
::x seq -10 10 0.5
vector ::y

set items {label variable to from digits resolution tickinterval gridpos}
set scale_cfg {
       a ::a  -0.31  0.3 5 0.001 0.1   1,1
       b ::b  -1.01  1.0 5 0.002 0.5   1,2
       c ::c  -4.01  4.0 4 0.01  2.0   1,3
       d ::d -10.01 10.0 3 0.1 5.0     1,4
}

foreach $items  $scale_cfg {
       set $variable 1.0
       trace variable $variable w compute

       set w .sc$label
       set label [ string totitle $label ]
       scale $w -label $label \
               -variable $variable -to $to -from $from \
               -digits $digits -resolution $resolution \
               -tickinterval $tickinterval \
               -bd 2 -relief groove
       table . $w $gridpos -fill y
}

# fill vector ::y
compute

.g element create Function -xdata ::x -ydata ::y -pixels 3
.g axis configure y -min -20 -max 20
.g grid configure -hide no -dashes { 2 2 }

# ready