Currently I have awk command to do linear interpolation

awk '
{
     P[$1]=$2
     I[i++]=$1
}
END {
     j=0; s=I[j]; t=I[j+1]
     for(i=m;i<=n;i++) {
          if(I[j+2] && i>t) {
               j++; s=I[j]; t=I[j+1]
          }
          print i, P[s]+(i-s)*(P[t]-P[s])/(t-s)
     }
} ' m=1 n=8 infile

#X Y
1 22.3125
4 22.5
8 22.1875

What do you mean by polynomial interpolation?

Polynomial interpolation is an interpolation that based on three value points (two previous points and next point). So, if we see the data, there are an ID 1, 4, and 8. So, we need to find out the value of 2, 3, 5, 6, and 7 based on value 1, 4, and 8. The formula is that
(((x-x2) * (x-x3)) / ((x1-x2) * (x1-x3))) * y1 + (((x-x1) * (x-x3)) / ((x2-x1) * (x2-x3))) * y2 + (((x-x1) * (x-x2)) / ((x3-x1) * (x3-x1))) * y3
x = current ID;
x1 = the first known ID (second previous known ID); ---> 1
x2 = the second known ID (first previous known ID); ---> 4
x3 = the third known ID (next known ID); ---> 8
y1 = the first known value (the value of ID x1)
y2 = the second known value (the value of ID x2)
y3 = the third known value (the value of ID x3)

How about this:

awk '
{ P[$1]=$2 ; m=$1>m?$1:m; x[NR]=$1 ; y[NR]=$2 }
END {
    for(i=1;i<=m;i++) {
       if (i in P) printf "%0.4f %0.4f\n", i, P[i];
       else printf "%0.4f %0.4f\n", i, \
           (((i-x[2]) * (i-x[3])) / ((x[1]-x[2]) * (x[1]-x[3]))) * y[1] + \
           (((i-x[1]) * (i-x[3])) / ((x[2]-x[1]) * (x[2]-x[3]))) * y[2] + \
           (((i-x[1]) * (i-x[2])) / ((x[3]-x[1]) * (x[3]-x[1]))) * y[3] ;
    }
}' infile

It is working but shows the wrong result, thus it remains dissolved. Any how, thanks.

Damn,

Here is a debug version that show the formula with expanded values, it might help us find the issue.

Note data file should not contain the heading ( #X Y ) line:

awk '
{ P[$1]=$2 ; m=$1>m?$1:m; x[NR]=$1 ; y[NR]=$2 }
END {
    for(i=1;i<=m;i++) {
       if (i in P) printf "%0.4f %0.4f\n", i, P[i];
       else { printf "%0.4f %0.4f\n", i, \
           (((i-x[2]) * (i-x[3])) / ((x[1]-x[2]) * (x[1]-x[3]))) * y[1] + \
           (((i-x[1]) * (i-x[3])) / ((x[2]-x[1]) * (x[2]-x[3]))) * y[2] + \
           (((i-x[1]) * (i-x[2])) / ((x[3]-x[1]) * (x[3]-x[1]))) * y[3] ;
           printf "   (((%f-%f) * (%f-%f)) / ((%f-%f) * (%f-%f))) * %f +\n",
             i,x[2],i,x[3],x[1],x[2],x[1],x[3],y[1];
           printf "   (((%f-%f) * (%f-%f)) / ((%f-%f) * (%f-%f))) * %f +\n",
             i,x[1],i,x[3],x[2],x[1],x[2],x[3],y[2];
           printf "   (((%f-%f) * (%f-%f)) / ((%f-%f) * (%f-%f))) * %f\n",
             i,x[1],i,x[2],x[3],x[1],x[3],x[1],y[3];
           printf "  = %f + %f + %f\n",
             (((i-x[2]) * (i-x[3])) / ((x[1]-x[2]) * (x[1]-x[3]))) * y[1],
             (((i-x[1]) * (i-x[3])) / ((x[2]-x[1]) * (x[2]-x[3]))) * y[2],
             (((i-x[1]) * (i-x[2])) / ((x[3]-x[1]) * (x[3]-x[1]))) * y[3] ;
        }
    }
}' infile

7.0000 16.2130
   (((7.000000-4.000000) * (7.000000-8.000000)) / ((1.000000-4.000000) * (1.000000-8.000000))) * 22.312500 +
   (((7.000000-1.000000) * (7.000000-8.000000)) / ((4.000000-1.000000) * (4.000000-8.000000))) * 22.500000 +
   (((7.000000-1.000000) * (7.000000-4.000000)) / ((8.000000-1.000000) * (8.000000-1.000000))) * 22.187500
  = -3.187500 + 11.250000 + 8.150510

GREAT. It is working. But how to declare if x=0, then y[x]=0. Because for y[3] and y[4], the x[1]=0, thus y[0]=0.

awk '
{ P[$1]=$2 ; m=$1>m?$1:m; x[NR]=$1 ; y[NR]=$2 }
END {
    for(i=1;i<=m;i++) {
       if (i in P) printf "%0.4f %0.4f\n", i, P[i];
       else { printf "%0.4f %0.4f\n", i, \
           (((i-x[2]) * (i-x[3])) / ((x[1]-x[2]) * (x[1]-x[3]))) * y[1] + \
           (((i-x[1]) * (i-x[3])) / ((x[2]-x[1]) * (x[2]-x[3]))) * y[2] + \
           (((i-x[1]) * (i-x[2])) / ((x[3]-x[1]) * (x[3]-x[2]))) * y[3] ;
           printf "   (((%f-%f) * (%f-%f)) / ((%f-%f) * (%f-%f))) * %f +\n",
             i,x[2],i,x[3],x[1],x[2],x[1],x[3],y[1];
           printf "   (((%f-%f) * (%f-%f)) / ((%f-%f) * (%f-%f))) * %f +\n",
             i,x[1],i,x[3],x[2],x[1],x[2],x[3],y[2];
           printf "   (((%f-%f) * (%f-%f)) / ((%f-%f) * (%f-%f))) * %f\n",
             i,x[1],i,x[2],x[3],x[1],x[3],x[2],y[3];
           printf "  = %f + %f + %f\n",
             (((i-x[2]) * (i-x[3])) / ((x[1]-x[2]) * (x[1]-x[3]))) * y[1],
             (((i-x[1]) * (i-x[3])) / ((x[2]-x[1]) * (x[2]-x[3]))) * y[2],
             (((i-x[1]) * (i-x[2])) / ((x[3]-x[1]) * (x[3]-x[2]))) * y[3] ;
        }
    }
}' infile