How to convert discrete system into continous time system.

my discrete system is of this type x1(k+1)=x1(k)+[1/3*(x2(k)-x1(k))]+[1/3*(x3(k)-x1(k))]; x2(k+1)=x2(k)+[1/3*(x3(k)-x2(k))]+[1/2*(x4(k)-x2(k))]+[1/3*(x1(k)-x2(k))]; x3(k+1)=x3(k)+[1/2*(x5(k)-x3(k))]+[1/3*(x1(k)-x3(k))]+[1/3*(x2(k)-x3(k))]; x4(k+1)=x4(k)+[1/2*(x2(k)-x4(k))]; x5(k+1)=x5(k)+[1/2*(x3(k)-x5(k))]; .i have run a for loop for this system and the system is converging in 20 iterations.how shall i convert this system in to continuous form as i have to make a simulink model for this system.