diff --git a/pi.go b/pi.go
index c123891415ba30063559c159406f8a350b45ff5e..783f67110e90dc249455d33091936f704db3932b 100644
--- a/pi.go
+++ b/pi.go
@@ -1,14 +1,16 @@
// 29 april 2021
-// If I get time, it would be fun to do the second uebung in go.
+// An example for the second Uebung in Struktur und Simulation.
// For the sake of speed, we can do all the numbers at once, put
-// them in arrays, rather than doing i/o on every step.
+// them in arrays, rather than doing i/o on every step. This is actually
+// necessary if we want to make plots. We have to store all the points.
// The plotting library I used does not draw to the screen. Bummer. One could
-// use the canvas in vggio, although that pulls in all of fyne.
+// use the canvas in vggio, although that pulls in all of the fyne library.
+// There is an egregious bug in the clipping of lines in plotter, so do
+// not use it. Use a scatter plot.
package main
import (
- "bufio"
"errors"
"flag"
"fmt"
@@ -16,13 +18,6 @@ import (
"math/rand"
"os"
"strconv"
-
- "gonum.org/v1/plot"
- "gonum.org/v1/plot/font"
- "gonum.org/v1/plot/plotter"
- "gonum.org/v1/plot/vg"
- "gonum.org/v1/plot/vg/draw"
- "gonum.org/v1/plot/vg/vgimg"
)
const (
@@ -30,18 +25,12 @@ const (
exitFailure
)
-const (
- sizeHrznt font.Length = 15 * vg.Centimeter
- sizeVert font.Length = 10 * vg.Centimeter
- nPointPlot = 1000
-)
-
-func breaker(x interface{}) {}
-
// usage prints out anything the caller gives us then bails.
func usage(e string) {
- u := "usage: pi seed nsteps nstep_nprint"
- fmt.Fprintln(os.Stderr, e+"\n"+u)
+ u := "usage: pi [flags] seed nsteps nstep_nprint"
+ if e != ""{
+ fmt.Fprintln(os.Stderr, e+"\n"+u)
+ }
flag.Usage()
os.Exit(exitFailure)
}
@@ -60,7 +49,7 @@ func getnums(cmdArgs cmdArgs) ([]float32, []float32) {
}
}
if inPoint[0] {
- inCnt[0] = 1
+ inCnt[0] = 1 // avoid divide by zero errors in loop
}
for i := 1; i < cmdArgs.nstep; i++ {
inCnt[i] = inCnt[i-1]
@@ -73,98 +62,20 @@ func getnums(cmdArgs cmdArgs) ([]float32, []float32) {
stdErr := make([]float32, cmdArgs.nstep) // standard error
for i := range inCnt {
- ptmp := float64(inCnt[i]) / float64(i+1) // do we need more precision ?
- qtmp := 1 - ptmp
+ ptmp := float64(inCnt[i]) / float64(i+1)
pi[i] = float32(4 * ptmp)
- stdErr[i] = float32(4 * math.Sqrt((ptmp*qtmp)/(float64(i+1))))
+ stdErr[i] = float32(4 * math.Sqrt((ptmp*(1-ptmp))/(float64(i+1))))
}
return pi, stdErr
}
// wrtTable prints out the table, as per the Uebung instructions
func wrtTable(cmdArgs cmdArgs, pi, stdErr []float32) {
- b := bufio.NewWriter(os.Stdout)
- b.WriteString(fmt.Sprintf("%8s %7s %7s %7s\n", "step", "pi", "err", "stderr"))
- defer b.Flush()
+ fmt.Printf("%8s %7s %7s %7s\n", "step", "pi", "err", "stderr")
for i := 0; i < cmdArgs.nstep; i = i + cmdArgs.nstepPrint {
e := math.Pi - pi[i]
- b.WriteString(fmt.Sprintf("%8d %.5f %.5f %.5f\n", i+1, pi[i], e, stdErr[i]))
- }
-}
-
-// addline saves us doing the same point copying, adding three times.
-func oneplot(y []float32) (*plot.Plot, error) {
- p := plot.New()
- points := make(plotter.XYs, len(y))
- for i, piV := range y {
- points[i] = plotter.XY{X: float64(i + 1), Y: float64(piV)}
- }
- if line, err := plotter.NewLine(points); err != nil {
- return nil, err
- } else {
- line.LineStyle.Width = 4
- p.Add(line)
- }
- return p, nil
-}
-
-// doplot makes a primitive plot without any interesting options
-// If no plotname is given, it means no plot is wanted. We have to rewrite the data
-// to fit to the plot function's expectations (x/y pairs).
-func doplot(pi, stdErr []float32, plotName string) error {
- if plotName == "" {
- return nil
- }
- const step = "step"
- pPi, err := oneplot(pi) // pi estimate
- if err != nil {
- return err
- }
- pPi.Title.Text = ""
- pPi.X.Label.Text = step
- pPi.Y.Label.Text = "π estimate"
-
- pStd, err := oneplot(stdErr) // std error
- if err != nil {
- return err
- }
- pStd.Title.Text = ""
- pStd.X.Label.Text = step
- pStd.Y.Label.Text = "std error"
-
- pAbs := plot.New()
- {
- tmperr := make([]float32, len(pi)) // the extra bracing makes
- for i := range tmperr { // the lifetime of tmperr clear...
- tmperr[i] = pi[i] - math.Pi // for garbage collector
- }
- pAbs, err = oneplot(tmperr)
- if err != nil {
- return err
- }
- }
- pAbs.X.Label.Text = step
- pAbs.Y.Label.Text = "error"
- dt := draw.Tiles{Rows: 3, Cols: 1, PadTop: 2}
- img := vgimg.New(vg.Points(600), vg.Points(500))
- dc := draw.New(img)
- dCnvs := plot.Align([][]*plot.Plot{{pPi}, {pStd}, {pAbs}}, dt, dc)
-
- pPi.Draw(dCnvs[0][0])
- pStd.Draw(dCnvs[1][0])
- pAbs.Draw(dCnvs[2][0])
- w, err := os.Create(plotName)
- if err != nil {
- return fmt.Errorf("Opening plotfile for writing %w", err)
- }
- defer w.Close()
- breaker("before vgimg")
- jpg := vgimg.JpegCanvas{Canvas: img}
- if _, err := jpg.WriteTo(w); err != nil {
- return err
+ fmt.Printf("%8d %.5f %.5f %.5f\n", i+1, pi[i], e, stdErr[i])
}
- pStd.Save(vg.Points(150), vg.Points(250), "foo.png")
- return nil
}
type cmdArgs struct {
@@ -178,8 +89,8 @@ type cmdArgs struct {
func cmdline(cmdArgs *cmdArgs) error {
var err error
var suppress bool
- flag.StringVar(&cmdArgs.plotName, "p", "", "Plot filename")
- flag.BoolVar(&suppress, "s", false, "Suppress stdout")
+ flag.StringVar(&cmdArgs.plotName, "p", "", "filename to Plot to. No name means no plofile")
+ flag.BoolVar(&suppress, "s", false, "Suppress stdout - the long table of numbers")
flag.Parse()
if flag.NArg() != 3 {
return errors.New("Wrong number of command line args")
@@ -201,7 +112,6 @@ func cmdline(cmdArgs *cmdArgs) error {
return nil
}
-// main. The rules say ./pi seed nsteps nstep_print
func main() {
var cmdArgs cmdArgs
if err := cmdline(&cmdArgs); err != nil {