I'm currently setting up my next grow. I'm currently perusing a double major in physics and mathematics, and thought it would be interesting to see if I could pin down a rough mathematical model for the daily growth of a marijuana plant, so that if conditions remain constant and everything goes as planned, you could predict, with a decent degree of accuracy, both the expected height of a plant and yield. Obviously, because of genetics, it is impossible to build a mathematical model (equation) that works for every strain. But this isn't a Thesis, it's just for my own entertainment, so I'm going to give it a shot.
The key to understanding how marijuana grows is understanding that it presents itself as an exponential function. In NON mathematical terms, this means that the rate of growth on any one day is contingent on the cumulative growth that had occurred on all prior days... To simplify it even further, as the plant continues to grow, the number of leaves that it has (and the size of those leaves) increases, which allows it to absorb more light than it did the day before, and thus accelerates the rate that it is growing... Each day, the rate that it grows becomes faster, which causes leaves to become larger and more numerous, and then those leaves absorb more light that causes them to grow faster than they did the day before...
This is why you see such little growth as a seedling in comparison to the last week of vegetative growth, and likewise, why you see such little bud growth in the first week after the first bud appears in comparison to the lady two weeks of flowering. I've read that nearly 30% of your total yield occurs in the last 14 days.... Building a mathematical model to predict growth would show that ONLY through an exponential equation.
I'm growing from bag seed, looking for a mother to cone, so that seems like a great opportunity to start collecting data on this, as I'll be starting with roughly 80 seedlings from a variety of mystery strains... The data is sure to show wide variation between this many plants, but there should be a general trend that can be found that could be considered fairly reliable under these conditions. Depending on what I find, I may do this a couple times with different conditions to compare rates of growth under different levels of watts/ft^2, and once the data is well rounded enough, a final mathematical model can be built to predict the size of a plant on any given day, based on any number of watts/ft^2 that you plug into the equation, and would even allow you to change the lighting throughout and predict the most efficient use of electricity to produce the maximum yield.
Or.... Maybe I just need to smoke a little bit more, because I'm taking this WAY too seriously. Lol. I enjoy it though.