Interactive plotting with Plotchart
Arjen Markus (1 april 2011) When you want to illustrate a mathematical procedure, such as curve fitting, having a graph handy is quite useful. Here is a small program that allows you to change a parameter and see the immediate effect on the function. Not a major breakthrough in mathematical education perhaps, but it does show how easy it really is.
Some notes:
- This was tested with Plotchart 1.8.2, newer versions ought to make the program even simpler.
- I found a bug in Plotchart, which necessitates to insert a dummy point for the "fit" data. I will solve that in the next release.
Here is a screen-shot:
# scale-plot.tcl --
# Demonstrate how a scale widget can interact with a plot
#
# Note:
# Tested with an older version of Plotchart. Hence the
# fiddling with the tags
#
package require Plotchart
# refreshPlot --
# Draw a new line to fit the data
#
proc refreshPlot {p value} {
#
# Clean up the old line
# (Still the only tag in this version of Plotchart)
#
.c delete data
$p plot fit {} {} ;# Make a clean break
#
# The new line
#
for { set i 0 } { $i < 20 } { incr i } {
set x [expr {-10.0 * ($i-10)}]
set y [expr {$value * $x}]
$p plot fit $x $y
}
}
#
# Set up the widgets
# Note:
# -from start at top
#
scale .s -from 10 -to -10 -variable param -resolution 0.1 -tickinterval 2
canvas .c -bg white -width 400 -height 300
grid .s .c -sticky news
set p [::Plotchart::createXYPlot .c {-10 10 5} {-20 20 10}]
#
# Connect the plot to the scale widget
#
.s configure -command [list refreshPlot $p]
#
# Introduce some data
#
$p dataconfig measured -colour blue -symbol cross -type symbol
$p plot measured 3.5 6.0
$p plot measured -2.5 -4.0
$p plot measured -1.5 0.05
$p plot measured 5. 4.05
#
# Remove the tag "data" - we want to keep the measured points
#
.c dtag data data
#
# Dummy data point - error otherwise
#
$p plot fit 0.0 0.0