taux = 2.5 (slider from 0 to 20, step 0.1)
r(x) = round(100.0 * x) / 100.0
f1(x) = r(x * (1.0 + taux / 100.0))
g(x) = r(x * (1.0 + taux / 100.0)^(20.0))
f2(x) = f1(f1(x))
f3(x) = f1(f2(x))
f4(x) = f1(f3(x))
f5(x) = f1(f4(x))
f6(x) = f1(f5(x))
f7(x) = f1(f6(x))
f8(x) = f1(f7(x))
f9(x) = f1(f8(x))
f10(x) = f1(f9(x))
f11(x) = f1(f10(x))
f12(x) = f1(f11(x))
f13(x) = f1(f12(x))
f14(x) = f1(f13(x))
f15(x) = f1(f14(x))
f16(x) = f1(f15(x))
f17(x) = f1(f16(x))
f18(x) = f1(f17(x))
f19(x) = f1(f18(x))
f20(x) = f1(f19(x))
e = If(x > 0.0, f20(x) - g(x), 0.0)