“…We let and where is transposition, then our differential Eq. (1) can be rewritten in a matrix form as where Now, using the third equation in model (1) , thus and deploying the method of integration factor and change of variables [33] , yields Next, we consider the fourth, fifth, sixth equation of model (1) and using the same above process, we have Hence, from [34] and [35] , we see that and provided with same ideas being valid for S ( t ), this guarantees that the state variable remain positive during the entire scope of the study [33] . Grounded on this, we can say that matrix M has all its off diagonal entries to be non-negative and that matrix M 1 ≥ 0, which proves the properties of Metzler matrix [33] , [36] .…”