 we will look at this second structure of the system. Now, one we have seen where the carrying capacity was involved and they affect resource adequacy. So, we had a positive feedback system generated negative feedback system. Now, so let us imagine that in a case of the population as well as the carrying capacity, we had defined both in the same terms right population carrying capacity we had similar units right. So, in that sense then carrying capacity can be assumed like a stock and births and total population is the stock. So, initially we want lot of people from the total pool to move towards the population and as this stock depletes then that is going to put a constraint on how much the resource system can grow. So, that is kind of a very broad explanation. So, we will model it and then we can look at the system better understand it. Let us take a very simple model of new product life cycle or new product diffusion. There are more complex models as we can maybe see later, but let us divide the population into just two distinct types non-owners and owners. You can imagine any new product like a cell phone or a cycle or watch or whatever it is bags anything. So, there are people who does not have the product and people have the products and for simplicity sake we will assume no births, deaths and migrations occur during this time which affects the population in a fixed location nothing is going to change and product population homogeneous interactions remain same among the population and people who buy it owns it indefinitely. So, we will make that assumption also and all the population is trying to purchase that same product or a similar kind of products. So, we will make that simple assumption. So, with that let us say building this model as it told let us assume two stocks one we have non-owners another we have owners. So, non-owners become owners if they buy the product right. So, the buying rate you can define a simple parameter called as buying rate moves the people from non-owners to owners. So, that is a rate which affects the non-owners and moves them into owners. The question is what affects the buying rate. So, let us go to the let us define non-owners owners. You can observe what you have done here I have taken a stock and connected to another stock through a rate. So, as you can see here as a buying rate increases the non-owners are going to come down the buying rate goes up non-owners are going to come down and as buying rate goes up owners are going to increase. So, that is a simple causal link that has been captured by this diagram. As you can observe there is no inflow into the non-owners right. That means, non-owners is fixed whatever the initial value is there only thing is get affected is a buying rate. So, non-owners should keep reducing as long as a buying rate is positive right as every period as long as the positive buying people buying it. So, those many non-owners are going to get converted into owners. Another you can observe is as it all in stocks matter is conserved. So, whoever non-owners gets depleted here the same amount get increased here as owners. So, matter is conserved is 5 people buy it that week. So, then non-owners reduces by 5 that week owners get increased by 5 the same that week. So, non-owners are starts as an initial value because owners will also start with some initial value and as buying rate increases non-owners are going to fall down. As buying rate increases owners are going to simple system that we have. Now, what affects this buying rate? There are various I think some more assumptions probably I have to list before I can ask you that question in all fairness. Let us write whatever comes to your mind. Cost or price? What else? Income. So, let us just then change it into something called as purchasing power that takes care of your income as well as the price of product etcetera. So, let us just get rid of that quality number of non-owners a number of owners. If lot of non-owners are there then buying rate should be higher if number of non-owners are low buying rate should be low. We are having marketing here two types of marketing right. One is the advertisement the other is through and other is through reviews. Advertisement other is reviews which part we are going to use the phrase called as word of mouth. The word of mouth we mean is a kind of when you hear positive reviews about a product then people are more tempted to buy it. Then whatever be the advertisement word of mouth finally will be the dominating factor in selling things. Advertisement can help in the initial sales beyond which word of mouth has to taken. Now word of mouth has been facilitated much better these days through social media. So, all your social media posts and positive or all your you know thumbs ups and smileys all are counted as part of word of mouth right. You can imagine like you know you can think of any movie initial advertisements may make you watch it. But within the second day word of mouth kicks in people either thrash it or they say it is good and then you go and watch it. So, among them this kind of dominates more than this one. And another good thing about this from the company point of view is word of mouth is free. So, as long as you get a good product and a good word out then social media and other sources will take care of the sales and you do not really need to do much advertisement. This is very expensive, this is very cheap. But it can be very critical and very cruel it may not go the way you want it to go, but still you want to get this out as soon as possible. The positive word of mouth both positive and negative that is initially worry about positive word of mouth. So, to keep the model simple we are going to only focus on this and this we will initially focus on this. So, we can come with a very basic model then we can expand the model and you know always try to bring in advertisements and other things as you go along.