Need better documentation for error bars

You shouldn't have to look at how the error bar plotter draws its lines to 
figure out how to pass data into the plotter.

BTW, the error values returned by the error interfaces is two positive numbers 
that the plotter automatically subtracts and adds to the middle value for you:

package main

import (
    "code.google.com/p/plotinum/plot"
    "code.google.com/p/plotinum/plotter"
)

type XYMeanErr []struct {
    X float64
    YMean, YError float64
}

func (e XYMeanErr) Len() int {
    return len(e)
}

func (e XYMeanErr) XY(i int) (x, y float64) {
    return e[i].X, e[i].YMean
}

func (e XYMeanErr) YError(i int) (float64, float64) {
    yerr := e[i].YError
    return yerr, yerr
}

func main() {
    data := XYMeanErr{
        {0, 10, 5}, {1, 10, 5}, {2, 20, 10},
    }

    p, err := plot.New()
    if err != nil {
        panic(err)
    }
    line, err := plotter.NewLine(data)
    if err != nil {
        panic(err)
    }
    yerr, err := plotter.NewYErrorBars(data)
    if err != nil {
        panic(err)
    }
    p.Add(line, yerr)
    p.Y.Min = 0
    if err := p.Save(4, 4, "test.eps"); err != nil {
        panic(err)
    }
}

Original issue reported on code.google.com by burns.ethan@gmail.com on 7 May 2014 at 11:29

zhanglong2005 / plotinum

Need better documentation for error bars #141