# normalCurve.frink

``` // This program draws the normal curve or "bell curve" used in statistics. // It's a bit slow because calculating inverseErf for very high sigmas is // quite slow. use statistics.frink plotNormal[mean, sigma, minSigma, maxSigma, g is graphics] := {    g.color[0.5,0.5,0.5]    vscale = 8 sigma^2           // Found experimentally to look good.    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 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]    steps = 1000    low = 1/1000                 // Use rational numbers so that the exactly    high = 999/1000              // right number of points is plotted.    wheel = 0    first = true    points = 0    for phi = high to low step ((low-high)/(steps-1))    {       z = inversePhi[phi,8]       x = mean + sigma * z       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, -.25, 1, 1]          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, 1, 1]       points = points+1    }    println["\$points points plotted."] } g = new graphics plotNormal[100, 15, -3.0902, 3.0902, g] g.show[] g.write["normal.svg", 800, 600] g.write["normal.png", 800, 600] ```

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 18491 days, 4 hours, 58 minutes ago.