Relative error in the sum of squares is at most `ftol'.

d_parent = - (alpha/beta) * ((time/beta) + 1)^-1 * parent

d_parent = - ((k1 * g * exp(-k1 * time) + k2 * (1 - g) * exp(-k2 * time)) / (g * exp(-k1 * time) + (1 - g) * exp(-k2 * time))) * parent

d_m1 = + f_parent_to_m1 * k_parent * parent - k_m1 * m1