func (lg *LinearSeq) WithStart(start float64) *LinearSeq {
	lg.start = start
	return lg
}
WithStart sets the start and returns the linear generator.
package chart
func LinearRange(start, end float64) []float64 {
	return Seq{NewLinearSequence().WithStart(start).WithEnd(end).WithStep(1.0)}.Values()
}
func LinearRangeWithStep(start, end, step float64) []float64 {
	return Seq{NewLinearSequence().WithStart(start).WithEnd(end).WithStep(step)}.Values()
}
func NewLinearSequence() *LinearSeq {
	return &LinearSeq{step: 1.0}
}
type LinearSeq struct {
	start float64
	end   float64
	step  float64
}
func (lg LinearSeq) Start() float64 {
	return lg.start
}
func (lg LinearSeq) End() float64 {
	return lg.end
}
func (lg LinearSeq) Step() float64 {
	return lg.step
}
func (lg LinearSeq) Len() int {
	if lg.start < lg.end {
		return int((lg.end-lg.start)/lg.step) + 1
	}
	return int((lg.start-lg.end)/lg.step) + 1
}
func (lg LinearSeq) GetValue(index int) float64 {
	fi := float64(index)
	if lg.start < lg.end {
		return lg.start + (fi * lg.step)
	}
	return lg.start - (fi * lg.step)
}