double-integral-hack.rb

def f(x,y)
	(((-0.0447 * x ** 6 + 0.2731 * x ** 5 - 0.7935 * x ** 4 + 1.7751 * x ** 3 - 2.561 * x ** 2 + 0.9885 * x + 1.0821) ** 2) - (y ** 2)) ** 0.5
end

startx = 0
endx = 2

starty = -1.2
endy = 1.2

PIECES = 1000000.0

xstep = (endx - startx) / PIECES
ystep = (endy - starty) / PIECES

area = xstep * ystep

sum = 0

xx = startx
yy = starty

while xx < endx
	while yy < endy
		tmp = f(xx,yy)
		sum += tmp unless tmp.is_a? Complex
		yy += ystep
	end
	xx += xstep
end

puts area * sum * PIECES

Noticed the problem. The higher PIECES is, the smaller the resulting value. The way to fix it is to change line 32 to be puts area * sum * PIECES.

I see. i'll correct.