Competitive inhibition model for single substrate and single inhibitor.
Names: Vmax, Km, Ki, Ic
Meanings: Vmax = Maximum enzyme velocity, Km = Michaelis-Menten constant, Ki = Inhibitor constant, Ic = Inhibitor concentration
Lower Bounds: Vmax > 0, Km > 0, Ki >0
Upper Bounds: none
Note that this function is usually used in global fit, Vmax, Km and Ki should be shared, and Ic be fixed for each dataset. The initial value of Ki can be the mean of Ic.