a = 1.3 (slider from -5 to 5, step 0.1)
x_s = -1 (slider from -5 to 5, step 0.1)
y_s = 0.7 (slider from -5 to 5, step 0.1)
c: y = a * (x - x_s)^(2.0) + y_s
A = Extremum(a * (x - x_s)^(2.0) + y_s)