```cpp
// AngelCAD
double f(double sign, double x, double n)
{
   double xn  = pow(x,n);
   double x1n = pow(1-x,n);
   return sign*(xn/(xn+x1n) + 0.5);
}

shape@ main_shape()
{
   double nv= 10;
   double n = 2;
   pos2d@[] v;
   for(double i=0   ; i<nv; i++) { v.push_back(pos2d(i/nv,f(-1,i/nv,n))); };
   for(double i=nv-1; i>=0; i--) { v.push_back(pos2d(i/nv,f(+1,i/nv,n))); };
   return linear_extrude(scale(8,1)*polygon(v),0.1);
}

void main()
{
   shape@ obj = main_shape();
   obj.write_xcsg(GetInputFullPath());
}
```