#/***********************************************************
#    atan.rb -- µÕ»°³Ñ´Ø¿ô
#***********************************************************/
N = 24
PI = 3.14159265358979323846264
LDBL_DIG = 18

def latan( x )
    if      (x >  1);  sgn =  1;  x = 1 / x
    elsif   (x < -1);  sgn = -1;  x = 1 / x
    else;              sgn =  0;  end
    a = 0
    N.downto(1) do |i|
        a = (i * i * x * x) / (2 * i + 1 + a)
    end
    if    (sgn > 0); return  PI / 2 - x / (1 + a)
    elsif (sgn < 0); return -PI / 2 - x / (1 + a)
    else;            return           x / (1 + a); end
end

printf("  x    %-*s  º¸¤Îtan\n", LDBL_DIG + 2, "¼«²ÈÀ½atan")
for i in -10..10 
    x = i / 4.0;  y = latan(x)
    printf("%5.2f  %*.*f  % g\n", x, LDBL_DIG + 2, LDBL_DIG - 1, y, Math::tan(y))
end

exit 0