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 20145 days, 12 hours, 8 minutes ago.