a = 1.5 (slider from -5 to 5, step 0.1)
x_s = 0.8 (slider from -5 to 5, step 0.1)
y_s = 1.2 (slider from -5 to 5, step 0.1)
f(x) = a * (x - x_s)^(2.0) + y_s