Correlation of liquid-liquid equilibrium data  |POLVER05_1
f(t12) = 1/(x1*x2)-2*t21*c2/((x1+x2*c1)^3)-2*t12*c4/((x2+x1*c3)^3)  #
f(t21) = (x1-x2)/((x1*x2)^2)+6*t21*c2*(1-c1)/((x1+x2*c1)^4)+6*t12*c4*(c3-1)/((x2+x1*c3)^4)  #
c1=exp(-alpha*t21)  #
c2=exp(-2*alpha*t21)  #
c3=exp(-alpha*t12)  #
c4=exp(-2*alpha*t12)  #
x2=1-x1  #
alpha=0.4  #
x1=0.5  #
t12(0)=1
t21(0)=10