Download or view normalCurve2.frink in plain text format
// This program draws the normal curve or "bell curve" used in statistics.
use statistics.frink
plotNormal[mean, sigma, steps, g is graphics] :=
{
low = 1/steps // Use rational numbers so that the exactly
high = 1-low // right number of points is plotted.
println["low is $low"]
minSigma = inversePhi[low, 8]
println["minsigma is $minSigma"]
maxSigma = inversePhi[high, 8]
println["maxsigma is $maxSigma"]
vscale = 8 sigma^2 // Found experimentally to look good.
ceilingH = normalDensity[mean + sigma * maxSigma, mean, sigma]
scaledCeilingH = ceilingH * vscale
r = scaledCeilingH
println["ceiling H is $ceilingH"]
println["scaled ceiling is $scaledCeilingH"]
g.color[0.5,0.5,0.5]
g.line[mean + (minSigma * sigma), 0, mean + (maxSigma * sigma), 0]
width = maxSigma - minSigma
// This polyline is the normal curve.
c = new polyline
for s=minSigma to maxSigma+0.001 step (width/100)
{
x = mean + (sigma * s)
y = -normalDensity[x, mean, sigma] * vscale
c.addPoint[x,y]
}
g.add[c]
g.color[0,0,0]
wheel = r/2
first = true
points = 0
for phi = high to low step ((low-high)/(steps-1))
{
// s = now[]
x = inversePhi[phi,100,15]
n = normalDensity[x, mean, sigma]
do
{
wheel = (wheel + 0.618034) mod 1
} while wheel > n
h = wheel
if first
{
g.color[1,0,0] // Draw the "you" circle in red.
g.fillEllipseCenter[x, -1/2 r, r, r]
g.color[0,0,0]
g.font["SansSerif", 4]
g.text["You are here.", x, 7]
g.line[x, 5, x, 1] // Arrow body
// Arrowhead
p=new filledPolygon
p.addPoint[x,.65]
p.addPoint[x+0.3,2.5]
p.addPoint[x-0.3,2.5]
g.add[p]
first = false
} else
g.fillEllipseCenter[x, -h*vscale, r, r]
points = points+1
// e = now[]
// println["point $points, time is " + format[e-s,"ms",3]]
}
println["$points points plotted."]
}
g = new graphics
points = 1000
// You can pass in a number of points as the sole argument.
if length[ARGS] > 0
points = eval[ARGS@0]
plotNormal[100, 15, points, g]
g.show[]
g.write["normal$points.svg", 1024, undef]
g.write["normal$points.png", 2000, undef]
g.write["normal$points.html", 800, undef]
//g.print[]
Download or view normalCurve2.frink in plain text format
This is a program written in the programming language Frink.
For more information, view the Frink
Documentation or see More Sample Frink Programs.
Alan Eliasen was born 19966 days, 20 hours, 48 minutes ago.