问如何用gnuplot绘制一条光滑的直线通过一系列的点？

EN

### plot cubix Bézier curve through given points
reset session

$Data <<EOD
0 0
2 3
4 2
9 3
5 7
3 6
4 5
5 5
4 4
1 6
1 4
3 10
EOD

set size ratio -1
set angle degrees
set key noautotitles reverse Left
set samples 200

colX     = 1
colY     = 2
j        = {0,1}                                 # imaginary unit
a(dx,dy) = dx==0 && dy==0 ? NaN : atan2(dy,dx)   # angle of segment between two points
L(dx,dy) = sqrt(dx**2 + dy**2)                   # length of segment
r        = 0.333                                 # relative distance of ctrl points

stats $Data u 0 nooutput   # get number of points+1
N = STATS_records+1
array P0[N]
array PA[N]
array PB[N]
array P1[N]

x1=x2=y1=y2=ap1=NaN
stats $Data u (x0=x1, x1=x2, x2=column(colX), i=int($0)+1, \
               y0=y1, y1=y2, y2=column(colY), P0[i]=x0+j*y0, \
               dx1=x1-x0, dy1=y1-y0, d1=L(dx1,dy1), dx1n=dx1/d1, dy1n=dy1/d1, \
               dx2=x2-x1, dy2=y2-y1, d2=L(dx2,dy2), dx2n=dx2/d2, dy2n=dy2/d2, \
               a1=a(dx1,dy1), a2=a(dx2,dy2), a1=a1!=a1?a2:a1, \
               ap0=ap1, ap1=a(cos(a1)+cos(a2),sin(a1)+sin(a2)), \
               PA[i]=x0+d1*r*cos(ap0) + j*(y0+d1*r*sin(ap0)), \
               PB[i]=x1-d1*r*cos(ap1) + j*(y1-d1*r*sin(ap1)), P1[i]=x1+j*y1, 0) nooutput
# add last segment
P0[i+1] = x1+j*y1
PA[i+1] = x1+d1*r*cos(ap1)+j*(y1+d1*r*sin(ap1))
PB[i+1] = x2-d2*r*cos(a2) +j*(y2-d2*r*sin(a2))
P1[i+1] = x2+j*y2

# Cubic Bézier function with t[0:1] as parameter between two points
# p0: start point, pa: 1st ctrl point, pb: 2nd ctrl point, p1: endpoint
p(i,t) = t**3 * (  -P0[i] + 3*PA[i] - 3*PB[i] + P1[i]) + \
         t**2 * ( 3*P0[i] - 6*PA[i] + 3*PB[i]        ) + \
         t    * (-3*P0[i] + 3*PA[i]                  ) + P0[i]

plot $Data u 1:2 w lp pt 7 lc "red" dt 3 ti "data", \
        '' u 1:2 smooth path w l lc "black" ti "smooth path", \
     for [i=2:|P0|] [0:1] '+' u (real(p(i,$1))):(imag(p(i,$1))) w l lc "blue" \
         ti i==2?("\nCubic Bézier\nthrough points"):''
### end of script

spline(x,x1,y1,x2,y2) = y1+x1**2*(y1-y2)*(3*x2-x1)/(x1-x2)**3 + 6*x1*x2*(y2-y1)/(x1-x2)**3*abs(x) + 3*(y1-y2)*(x1+x2)/(x1-x2)**3*abs(x)**2 + 2*(y2-y1)/(x1-x2)**3*abs(x)**3

$Data <<EOD
0 0
2 3
4 2
9 3
5 7
3 6
4 5
5 5
4 4
1 6
1 4
3 10
EOD

stats $Data noout
array xvals[STATS_records]
array yvals[STATS_records]
do for [i=1:|xvals|] {
  stats $Data every ::i-1::i-1 u (xvals[i]=$1,yvals[i]=$2) noout
}

plot $Data w lp pt 7 lc "red" dt 3,\
 for [i=1:|xvals|-1] [xvals[i]:xvals[i+1]] spline(x,xvals[i],yvals[i],xvals[i+1],yvals[i+1]) lc "blue" not,\
 keyentry w l lc "blue" t "user-defined splines",\
 $Data smooth path lc "black" t "smooth path"

plot $Data w lp pt 7 lc "red" dt 3,\
 for [i=1:|$Data|-1] [word($Data[i],1):word($Data[i+1],1)] spline(x, real(word($Data[i],1)), real(word($Data[i],2)), real(word($Data[i+1],1)), real(word($Data[i+1],2)) ) w l lc "blue" not,\
 keyentry w l lc "blue" t "user-defined splines",\
 $Data smooth path lc "black" t "smooth path"