For a function of two variables z=f(x,y), the gradient is the two-dimensional vector <f_x(x,y),f_y(x,y)>. This definition generalizes in a natural way to functions of more than three variables. For the function z=f(x,y)=4x^2+y^2.
By this definition, about 10% of people who smoke marijuana become addicted to it. (More on Time.com: PHOTOS â Cannabis Conventions). However, nonspecialists (including many doctors) still tend to use an older perspective, now seen as outdated by experts.
Unsurprisingly to marijuana lovers around the world, there has yet to be a single reported death linked to cannabis overdose. In fact, you would have to consume 20,000 to 40,000 times your average dose in order for marijuana to kill you. That would be about 1,500 pounds of marijuana in 15 minutes.