function e=rminfal(c,k)
% rminf: used to find the minimum reflux ratio in ideal binary distillation
% function e=rminfal(c,k)
%  c: alpha, xf, q
x1=((c(1)/k)-1)/(c(1)-1);
x2=c(2)/(1+(k-1)*c(3));
e=x1-x2;
