6.9(a) ESTIMATING MODEL PARAMETERS INVOLVING ODE’S USING FERMENTATION DATA |POLVER05_0 |1
d(y1)/d(t) = b1 * y1 * (1 - y1 / b2)
d(y2)/d(t) = b3 * y1 - b4 * y2
b1 = 0.1
b2 = 4
b3 = 0.02
b4 = 0.02 
y1(0) = 0.18
y2(0) = 0
t(0) = 0
t(f) = 190