#/***********************************************************
#    newton.c -- Newton (ニュートン) 補間
#***********************************************************/
N = 5
$x = [ 0, 10, 20, 30, 40 ]
$y = [ 610.66, 1227.4, 2338.1, 4244.9, 7381.2 ]       # データ 
$a = []; N.times { $a.push(0) }                       # 補間多項式の係数 

def maketable
    $w = []; N.times { $w.push(0) }

    for i in 0...N
        $w[i] = $y[i]
        (i - 1).downto(0) do |j|
            $w[j] = ($w[j + 1] - $w[j]) / ($x[i] - $x[j])
        end
        $a[i] = $w[0]
    end
end

def interpolate( t )
    p = $a[N - 1]
    (N - 2).downto(0) do |i|
        p = p * (t - $x[i]) + $a[i]
    end
    return p
end

maketable
for i in 10..30
    printf("%3d %6.1f\n", i, interpolate(i))
end

exit 0