# File structures/Boundaries.rb, line 97
  def removeKnot(u)
    i,p = @spline.getIP(u)

    ## If i==0 then someone is doing something bad
    raise "Cannot remove d0 vertex knot u=#{u}" if i==0
    newDPoint = (@spline.d[i-1] + @spline.d[i+2])*0.5
    newD = [@spline.d.slice(1..(i-1)),newDPoint,@spline.d.slice((i+2)..(@spline.d.length-2))].flatten

    newK = [@spline.k.slice(0..i-1),@spline.k.slice((i+1)..(@spline.k.length-1))].flatten
    if @spline.closed
      @spline = QBSpline.new(newD, true,newK)
    else
      points = [@spline.d.first, newD, @spline.d.last].flatten
      @spline = QBSpline.new(points,false,newK)
    end
  end