線形補間 (1次元)

     y = (y2-y1)/(x2-x1)*(x-x1)+y1

  subroutine intpl(x1,x2,y1,y2,x,y)

  real,intent(in)::x1,x2,y1,y2,x

  real,intent(out):y

  y = (y2-y1)/(x2-x1)*(x-x1)+y1

  return

  end subroutine intpl